Polyester film for release films, polyester film roll for release films, and method for producing polyester film roll for release films

Abstract

To provide a polyester film for release films that retains the surface properties and easy inspectability suitable as the polyester film for release films, while having an excellent slit property, with reduced adhesion of chips to the film.SOLUTION: A polyester film for release films is a polyester film composed of two or more layers, with a surface specific resistance value of 1.0×109 Ω / sq. or more and 1.0×1012 Ω / sq. or less. A layer having a surface (layer A) contains organic particles of 0.75 mass% or more and 1.0 mass% or less, and a layer different from the layer A (layer B) contains organic particles of 0.01 mass% or more and 0.1 mass% or less, with a haze of 7% or more and 13% or less and an arithmetic average roughness of 20 nm or more and 30 nm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film for use as a release film. [Background technology]

[0002] Polyester films are used in a variety of industrial fields due to their excellent processability. For example, films that use a polyester layer as a substrate and have a releasable resin layer (a layer formed by applying a silicone resin, epoxy resin, or the like) are suitable for use in release applications.

[0003] Release films based on polyester layers are used for various release applications, such as ceramic green sheet production, LCD polarizer release, and photoresist release. Typical release films are required to minimize lamination misalignment and defects when a release target is placed on the film, as well as to ensure good releasability between the release film and the target. Furthermore, the presence of foreign matter on the film can cause uneven coating or missing coatings during resin layer application, so reducing foreign matter on the film is highly desirable. Examples of foreign matter adhering to release films include chips generated during film slitting. In particular, in polarizer release applications, chips are detected as bright spots during crossed Nicols testing, which is performed while the release film is still attached to the polarizer, so reduction is essential. Meanwhile, because inspections using reflected and transmitted light are also performed, it is also necessary to adjust the film haze of the release film to a suitable range. Patent documents 1 and 2 describe techniques for improving the slittability of polyester film, specifying the thickness and particle content of the polyester film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-204177 [Patent Document 2] Japanese Patent Application Publication No. 08-036739 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while the technology described in Patent Document 1 achieves improved slitting performance by limiting the particle content to a small range, this technology is only applicable to thin, smooth-surfaced films. In the case of release films, simply reducing the particle content reduces surface roughness and haze, impairing transportability, releasability, and ease of inspection. Furthermore, the technology described in Patent Document 2 uses inorganic particles with high hardness, which accelerates wear on the slit blade and leads to poor slitting performance. Furthermore, inorganic particles tend to aggregate and form coarse particles, which are detrimental to both slitting performance and inspection performance.

[0006] An object of the present invention is to overcome the drawbacks of the prior art, that is, to provide a polyester film for use as a release film that has good slittability and suppresses adhesion of chips to the film while maintaining good surface properties and easy inspectability as a release polyester film. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following configuration.

[0008] A polyester film consisting of two or more layers, with a surface resistivity of 1.0 x 10 9 Ω / □ or more 1.0×10 12 A polyester film for release film, having a surface roughness of Ω / □ or less, a layer (layer A) having a surface containing organic particles at 0.75% by mass or more and 1.0% by mass or less, a layer (layer B) different from layer A containing organic particles at 0.01% by mass or more and 0.1% by mass or less, a haze of 7% or more and 13% or less, and an arithmetic mean roughness of 20 nm or more and 30 nm or less.

[0009] A polyester film roll made of the polyester film described above, wherein the amount of foreign matter adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the outermost end of the polyester film roll is 75 μm or less. 2 / m 2 A polyester film roll for release film, which is as follows:

[0010] The method for producing the above-described release polyester film roll includes a cutting step of cutting the transport film with a cutting device equipped with a circular blade that rotates in the same direction as the transport direction of the transport film, and the depth of the circular blade in the cutting step is different when the transport speed of the transport film increases or decreases and when the transport speed is stable. [Effects of the Invention]

[0011] The polyester film for release film of the present invention has favorable inspectability and releasability, and also has good slittability, making it possible to suppress the amount of chips adhering to the film. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram schematically showing a method for measuring the amount of foreign matter (amount of chips) adhering to a film surface. [Figure 2] FIG. 1 is a graph showing the volumetric particle size distribution of Example 1 (solid line) and Comparative Example 1 (dotted line). [Figure 3] FIG. 1 is a diagram showing a schematic cross section of a slit in Example 1 (left) and Comparative Example 8 (right). DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below.

[0014] The polyester film for release film of the present invention is a polyester film consisting of two or more layers, and has a surface resistivity of 1.0 × 10 9 Ω / □ or more 1.0×10 12The polyester film for release film has a resistivity of Ω / □ or less, a layer having a surface (Layer A) containing organic particles in an amount of 0.75% by mass to 1.0% by mass, a layer different from Layer A (Layer B) containing organic particles in an amount of 0.01% by mass to 0.1% by mass, a haze of 7% to 13% and an arithmetic mean roughness of 20 nm to 30 nm. The polyester film is preferably a biaxially oriented polyester film.

[0015] The polyester according to the present invention comprises a dicarboxylic acid component and a diol component. In this specification, the term "component" refers to the smallest unit obtainable by hydrolysis of a polyester. The polyester is preferably one or more selected from polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, polypropylene terephthalate, polybutylene terephthalate, and poly-1,4-cyclohexylenedimethylene terephthalate. These materials are inexpensively available and have good film-forming properties, making them suitable for use. The polyester may be a homopolymer or a copolymer.

[0016] In order to carry out the present invention, it is preferable to use terephthalic acid as the dicarboxylic acid component constituting the polyester in an amount of 30 mol % or more based on the total dicarboxylic acid components. Examples of dicarboxylic acid components other than terephthalic acid include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid; alicyclic dicarboxylic acids such as adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid; aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorene acid; and ester derivatives thereof.

[0017] Examples of diol constituents constituting such polyesters include, but are not limited to, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol; alicyclic diols such as cyclohexanedimethanol, spiroglycol, and isosorbide; diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis(4-hydroxyphenyl)fluorene, and aromatic diols; and diols in which multiple units of the above-mentioned diols are linked together.

[0018] The polyester according to the present invention can be produced by a known method. Specifically, the esterification step is carried out using one or more esterification reaction vessels under stirring. For example, when a single esterification reaction vessel is used, the reaction temperature is usually 240 to 280°C, the relative pressure to atmospheric pressure is usually 0 to 400 kPa, and the reaction time is usually 1 to 10 hours. The esterification reaction rate of the esterification reaction product obtained in the esterification step is usually 95% or more.

[0019] The melt polycondensation step can usually be carried out continuously or batchwise using one or more polycondensation reaction vessels, and is carried out while gradually reducing the pressure from normal pressure and distilling the ethylene glycol produced under heating and stirring out of the system. For example, in the case of a batchwise method using a single polycondensation reaction vessel, the reaction temperature is usually 250 to 290°C, the final absolute pressure, which is gradually reduced from normal pressure, is usually 1.3 to 0.013 kPa (10 to 0.1 Torr), and the reaction time is usually 1 to 20 hours.

[0020] The intrinsic viscosity (IV) of the polyester resin can be determined by the polymerization end point based on the stirring torque of the polymer. When the stirring torque is high, the melt viscosity of the polymer increases, and so does the intrinsic viscosity. The stirring torque for determining the end point of the polymerization apparatus can be set to achieve the target intrinsic viscosity. In the present invention, it is preferable to set the stirring torque for determining the end point so that the IV of the film is 0.60 or more and 0.70 or less. By setting the torque in this range, it is easy to control the surface roughness, which is preferable.

[0021] The resulting polyester resin after polymerization is discharged in the form of strands from the bottom of the polymerization apparatus and cut with a cutter while being cooled with water. The chip shape can be controlled by cutting, so that polyester chips having a preferred bulk density can be obtained in the present invention.

[0022] The polycondensation reaction catalyst used may be one or more of antimony trioxide, antimony pentoxide, antimony acetate, antimony glycolate, germanium dioxide, organotitanium compounds, etc. Among these, antimony trioxide is preferred from the viewpoints of the transparency of the polyester obtained and availability.

[0023] The surface resistivity of the polyester film for release film of the present invention is 1.0 × 10 9 Ω / □ or more 1.0×10 12 The surface resistivity is preferably 5.0×10 or less. This range allows for good inspection properties, slitting properties, and chip adhesion to the film. 9 Ω / □ or more 5.0×10 10 The surface resistivity is in the range of 1.0×10 Ω / □ or less. 12 If it exceeds Ω / □, a sufficient antistatic effect cannot be obtained, and the amount of chips adhering to the film increases.

[0024] In order to set the surface resistivity within the above range, it is preferable to incorporate an antistatic agent into the film and adjust the amount added. The antistatic agent is added to an article to reduce static electricity in the article, and known agents can be used. If the amount of antistatic agent is too high, the surface resistivity will be 1.0 x 10 9 Although the resistivity falls below Ω / □ and the amount of chips adhering to the film is reduced, the increase in gelled matter may worsen inspectability. Also, if the amount of antistatic agent is low, the particle content must be increased to adjust the haze, which may accelerate wear on the slitting blade and worsen slitting performance.

[0025] In terms of heat resistance, anionic and nonionic antistatic agents are preferred. Examples of anionic antistatic agents include polymeric antistatic agents composed of one or more polymers of unsaturated monomers having sulfonate groups (e.g., sodium vinyl sulfonate, sodium methacrylate, sodium styrene sulfonate, etc.), and low-molecular-weight antistatic agents such as alkyl sulfonates (e.g., sodium pentanesulfonate, sodium octanesulfonate, etc.), aryl sulfonates (e.g., sodium benzylsulfonate, sodium toluylsulfonate, etc.), and aromatic sulfonates having alkyl groups (e.g., sodium dodecylbenzenesulfonate, etc.). Examples of nonionic antistatic agents include glycerin fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, N,N-bis(2-hydroxyethyl)alkylamines, N-2-hydroxyethyl-N-2-hydroxyalkylamines, polyoxyethylene alkylamines, polyoxyethylene alkylamine fatty acid esters, and alkyldiethanolamides. In particular, sodium dodecylbenzenesulfonate is preferred in terms of suppressing the generation of agglomerated foreign matter and facilitating inspection.

[0026] The polyester film for release film of the present invention preferably contains substantially no inorganic particles but organic particles. Incorporating inorganic particles into a release polyester film can improve the film's releasability and transportability, and can adjust the film haze to improve inspectability. However, the inorganic particles contained in the film may aggregate and become foreign matter inside the film, potentially impairing crossed-nicol inspectability. Furthermore, inorganic particles have high hardness, which can easily damage the slit blade used for film slitting, increasing the frequency of slit blade replacement and causing chip adhesion to the film, which can be undesirable from the standpoints of cost and quality. On the other hand, organic particles are less likely to form aggregates and have lower hardness than inorganic particles, making them less likely to damage the slit blade and resulting in excellent slitting properties. In the present invention, "substantially free of inorganic particles" means that the inorganic particle content is 0.05% by mass or less of the total film. A content of 0.03% by mass or less is particularly preferred.

[0027] The release polyester film of the present invention has a laminated structure of two or more layers. By changing the amount of organic particles contained in at least one surface layer (Layer A), the arithmetic mean roughness of the film surface can be adjusted, thereby improving releasability and transportability. When Layer A is present on at least one surface layer, the arithmetic mean roughness of the surface having Layer A is preferably 20 nm or more and 30 nm or less, more preferably 22 nm or more and 28 nm or less. When the arithmetic mean roughness of the film surface is within this range, better releasability and transportability can be achieved.

[0028] The release polyester film of the present invention preferably has a three-layer structure. A three-layer structure is advantageous in terms of cost because it is easy to mix and use recycled raw materials from edge portions generated during the film-forming process or recycled raw materials from other film-forming processes into a layer (Layer B) different from Layer A, as long as the mixed materials do not adversely affect the film properties. When the release polyester film of the present invention has a three-layer structure, the film haze can be adjusted by incorporating particles and an antistatic agent into Layer B. In this case, it is preferable that the film contains substantially no inorganic particles and contains organic particles, from the viewpoint of ensuring crossed Nicol inspection properties and slitting properties.

[0029] The total thickness of the release polyester film of the present invention is preferably 20 μm or more and 50 μm or less, more preferably 25 μm or more and 40 μm or less. In the case of a laminated structure, the total thickness of Layer A is preferably 1.5 μm or more and 3.5 μm or less. If the total thickness of Layer A is 1.5 μm or less, the arithmetic mean roughness becomes 20 nm or less, which may be undesirable as it impairs transportability and releasability. If the thickness is 3.5 μm or more, the amount of particles added increases, which accelerates wear of the slit blade, which may be undesirable in terms of slitting ability and cost.

[0030] The organic particles contained in the polyester film of the present invention may be of the same or different types. Examples of organic particles include crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester resin particles, polyimide particles, and melamine resin particles. The organic particle content of at least one surface layer (Layer A) is preferably 0.75% by mass to 1.0% by mass relative to 100% by mass of Layer A. If Layer A contains more than 1.0% by mass of organic particles, the particle count increases, which may be undesirable in terms of slitting properties. If the organic particle content is less than 0.75% by mass, the surface roughness and film haze may decrease, resulting in impaired transportability, releasability, and inspectability. Layer B preferably contains organic particles in an amount of 0.01% by mass to 0.1% by mass. Since Layer B does not require an arithmetic mean roughness, it is preferable to reduce the particle count as much as possible in terms of slitting properties, and it is preferable that the particle content of Layer A is greater than that of Layer B. For all particles, it is preferable that the volume average diameter is 1.2 μm or less, and that the particle shape and volume-based particle size distribution are uniform. If the volume average diameter is larger than 1.2 μm and the particle shape and volume-based particle size distribution are non-uniform, it becomes difficult to control the surface roughness of the polyester film, which may result in uneven coating or coating gaps.

[0031] The release polyester film of the present invention preferably has a film haze of 7% or more and 13% or less. When the polyester film of the present invention is used for polarizing plate release, an inspection using transmitted light or an inspection using reflected light may be performed. If the film haze of the polyester film exceeds 13%, the transmitted light may not be sufficiently transmitted in an inspection using transmitted light, which may cause an impediment to the inspection. On the other hand, if the film haze is less than 7%, the reflected light may be transmitted in an inspection using reflected light, which may cause an impediment to the inspection.

[0032] In a volumetric particle size distribution plotted with particle diameter on the horizontal axis and particle abundance on the vertical axis, the organic particles contained in the release polyester film of the present invention preferably have a maximum peak of 30% or more in the range of 0.5 μm to 1.2 μm, and an abundance ratio of 1.2 μm or more of 30% or less. It is particularly preferred that the maximum peak of 40% or more in the range of 0.5 μm to 1.2 μm, and an abundance ratio of 1.2 μm or more of 25% or less. If the maximum peak of 0.5 μm to 1.2 μm is less than 30% and the abundance ratio of 1.2 μm or more is greater than 30%, the amount of aggregated organic particles increases, resulting in greater variation in volume average particle diameter, making it difficult to control surface roughness and potentially causing coating unevenness or coating voids.

[0033] The polyester film roll for release film of the present invention is a polyester film roll made of the polyester film described above, wherein the amount of foreign matter adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the outermost end in the width direction of the polyester film roll is 75 μm 2 / m 2 The following is the result.

[0034] The method for measuring the amount of foreign matter adhering to the film surface is described in the section on measurement methods.

[0035] The amount of foreign matter adhering to the film surface is 75 μm 2 / m 2 It is preferable that the thickness is 65 μm or less. 2 / m 2 Most of the foreign matter adhering to the film surface is chips generated when cutting polyester film. 2 / m 2 If the amount is greater than this, many bright spot defects caused by chips may be detected during crossed Nicols inspection, which may result in a deterioration in inspectability.

[0036] The method for producing the polyester film for release film and the polyester fill roll for release film of the present invention will be described below. However, the present invention should not be construed as being limited to the products obtained by the following examples.

[0037] The polyester film of the present invention can be obtained by a method having the following steps. (Step 1) A step of melt-extruding a polyester resin into a sheet, contacting the melt-extruded polyester resin into a sheet on a casting roll at 18 to 50°C for 1 to 15 seconds to cool and solidify it, thereby obtaining an unstretched polyester film having a thickness of 180 to 1400 μm. (Step 2) A step of stretching the unstretched polyester film obtained in (Step 1) in the longitudinal direction at a stretching ratio of 2.5 to 5 times, and then cooling to obtain a uniaxially stretched polyester film. (Step 3) A step in which the uniaxially stretched polyester film obtained in (Step 2) is stretched in the width direction at a stretching ratio of 3 to 6 times, which is higher than the stretching ratio in the longitudinal direction, and then cooled to obtain a biaxially stretched polyester film. (Step 4) A step of heat-treating the biaxially stretched polyester film at a heat treatment temperature of 180 to 230°C to obtain a biaxially oriented polyester film. (Step 5) A step of slitting the biaxially oriented polyester film in a cutting process having a cutting device capable of changing the blade depth during cutting and a dust removal device for the slitting blade, so that the blade depth varies depending on whether the slitting speed is increased or decreased or kept constant, within the range of a tangent angle of the circular blade satisfying the conditions of 15 degrees or more and 25 degrees or less, to obtain a biaxially oriented polyester film roll.

[0038] Each step will be described in detail below.

[0039] (Step 1) Creating unstretched film The polyester resin is dried as necessary and fed to an extruder for melt extrusion. To achieve the intrinsic viscosity of the film within the aforementioned range, the average intrinsic viscosity of the polyester resin fed to the extruder is preferably 0.55 to 0.64 dL / g, more preferably 0.55 to 0.62 dL / g. The variation in the intrinsic viscosity of the polyester resin fed to the extruder is preferably 0.002 to 0.030 dL / g, more preferably 0.005 to 0.030 dL / g. The variation in the intrinsic viscosity of the polyester resin fed to the extruder is calculated as the standard deviation σ of the intrinsic viscosity of 50 samples randomly selected from the polyester resin fed to the extruder as a raw material. By providing a certain variation in the intrinsic viscosity of the polyester resin fed as a raw material, it is possible to increase the crystal plane orientation index of the film while reducing the orientation angle. If the intrinsic viscosity variation of the polyester resin supplied as raw material is less than 0.002 dL / g, the crystal plane orientation index χi value will be low, and it may be impossible to reduce bright spot defects. On the other hand, if the intrinsic viscosity variation of the polyester resin supplied as raw material is more than 0.030 dL / g, the properties of the resulting biaxially oriented polyester film will be unstable, and the orientation angle will be high, which may increase light leakage when inspecting polarizing plates using the crossed Nicols method, hindering the inspection. In terms of crossed Nicols inspection, it is preferable that the orientation angle be 5 degrees or less.

[0040] The method for keeping the variation of the polyester resin supplied as a raw material within the above range is not particularly limited. When the polyester resin supplied as a raw material is polymerized by a batch polymerization method, the variation of the intrinsic viscosity becomes larger than when it is polymerized by a continuous polymerization method.

[0041] The polyester resin melt-extruded by the extruder is then filtered through a filter. Because even small foreign particles can cause film defects, it is effective to use a high-precision filter that can capture 95% or more of foreign particles 5 μm or larger. The molten polyester resin undergoes thermal decomposition and hydrolysis, which breaks its molecular chains and reduces its intrinsic viscosity. The temperature and moisture content of the polyester resin during melt extrusion are not particularly limited as long as the intrinsic viscosity of the final film can be within the above-mentioned ranges. However, for stable melt extrusion, the temperature is preferably +5 to +40°C above the melting point of the polyester resin, and the moisture content is preferably 300 ppm or less.

[0042] The polyester resin is then formed into a sheet using a T-shaped die or the like, and the sheet-shaped polyester resin is cooled and solidified on a casting roll to obtain an unstretched film. In this case, the casting roll temperature is preferably 18 to 50°C, and the cooling time during which the sheet-shaped polyester resin contacts the casting roll is preferably 1 to 15 seconds. If the casting roll temperature is below 18°C, condensation is likely to form on the casting drum, which may result in poor film formability. If the casting roll temperature exceeds 50°C, the crystal plane orientation index χi value may be low. This is because a high casting roll temperature reduces cooling efficiency, resulting in the formation of microcrystals in the resulting unstretched film, which facilitates crystal orientation in the subsequent stretching process. Similarly, if the cooling time during contact with the casting roll is less than 1 second, the cooling efficiency is reduced, resulting in the formation of microcrystals in the resulting unstretched film, which tends to result in a low crystal plane orientation index χi value. The cooling time by the casting roll can be extended by increasing the diameter of the casting roll or reducing the line speed, but in consideration of facility space and productivity, the upper limit is 15 seconds. More preferably, the temperature of the casting roll is 20 to 30°C, and the cooling time during which the polyester resin formed into a sheet comes into contact with the casting roll is 3 to 12 seconds.

[0043] The thickness of the unstretched film obtained in step 1 is preferably 180 to 1400 μm. If the thickness of the unstretched film is less than 180 μm, the film thickness is insufficient to stretch the film so that the orientation angle and heat shrinkage rate fall within the desired range, and film tearing may occur during stretching. On the other hand, if the thickness of the unstretched film exceeds 1400 μm, uneven cooling occurs in the thickness direction when the polyester resin sheet is cooled and solidified on a casting roll, tending to lower the crystal plane orientation index χi value. Furthermore, the final thickness of the biaxially oriented polyester film may fall outside the range suitable for polarizing plate release applications.

[0044] (Step 2) Creating uniaxially stretched film The unstretched film obtained in step 1 is stretched in the longitudinal direction at a stretch ratio of 2.5 to 5.0 and then cooled to obtain a uniaxially stretched polyester film. The longitudinal stretching is preferably performed in a single step or multiple steps at a stretching temperature of 90 to 130°C. To prevent bowing and thickness unevenness in the longitudinal direction of the film, the stretching temperature is more preferably 100 to 120°C and the stretching ratio is more preferably 3 to 4. To prevent stretching unevenness and scratches, stretching is preferably performed in two or more steps. Furthermore, while longitudinal stretching causes shrinkage in the width direction, it is preferable that the width shrinkage of the film from this stretching step to the cooling step be 15% or less. If the width shrinkage of the film exceeds 15%, the film may meander or vary in width, or the uniformity of the plane orientation in the width direction of the film may deteriorate, making it difficult to achieve a crystal plane orientation index χi value of 6.0 or more over a 5-m width. The width shrinkage of the film can be controlled by adjusting the thickness profile of the film edge before longitudinal stretching or by adjusting the stretching tension using nip rolls or the like. The width shrinkage of the film shown here is calculated by dividing the difference between the film width immediately before the longitudinal stretching step and the film width after stretching and cooling by the film width immediately before the longitudinal stretching step. A film temperature of 25 to 45°C in the cooling step in (Step 2) is preferred for stable width stretching in the subsequent (Step 3).

[0045] (Step 3) Creating biaxially stretched film The uniaxially stretched polyester film obtained in the above (step 2) is stretched in the width direction at a stretch ratio of 3.0 to 6.0 times, which is higher than the stretch ratio in the longitudinal direction. The width direction stretching is preferably performed at a stretching temperature of 90 to 130°C. When the stretching temperature is lower than 90°C and the stretch ratio is higher than 6.0 times, the orientation angle tends to decrease, but the film becomes more susceptible to breakage and the crystal plane orientation index χi value decreases. The stretching temperature is more preferably 100 to 120°C and the stretch ratio is more preferably 4.0 to 5.0 times. Furthermore, to reduce the orientation angle, the stretch ratio in the width direction is preferably higher than the stretch ratio in the longitudinal direction. If the stretch ratio in the longitudinal direction is higher than the stretch ratio in the width direction, the molecular orientation in the film will be tilted toward the longitudinal direction, making it difficult to suppress the orientation angle variation.

[0046] In producing the biaxially oriented polyester film of the present invention, the stretching in the longitudinal direction is followed by the stretching in the width direction, because if the stretching in the longitudinal direction is carried out after the stretching in the width direction, the molecules will be strongly oriented mainly in the width direction after the first stretching in the width direction, but if the stretching in the longitudinal direction is carried out thereafter, the molecules will also be oriented in the longitudinal direction, resulting in a high orientation angle.

[0047] The film stretched in the width direction is then cooled at a film temperature of 25 to 45°C and a film width shrinkage rate of 0.1 to 20% / min to obtain a cooled biaxially stretched polyester film. A film temperature of 25 to 45°C in the cooling step is preferred because it suppresses relaxation of orientation in the width direction due to width shrinkage and prevents bowing. A temperature of 30 to 40°C is more preferred. If the film temperature in the cooling step is higher than 45°C, tension due to film width shrinkage may affect film formability, and the effect of suppressing relaxation of orientation in the width direction may not be fully achieved. If the film temperature in the cooling step is cooled to less than 20°C, productivity may be reduced.

[0048] Methods for cooling polyester film include air-cooling using a tenter where heat treatment is performed, air-cooling using aluminum or other shielding plates above and below the heat treatment area to block hot air, and cooling using rolls. In the air-cooling method using a tenter where heat treatment is performed, all zones are connected in the longitudinal direction, so the free flow of hot air, such as accompanying air currents, can cause temperature differences across the top and bottom of the film and across the width, making it difficult to sufficiently cool the film. In such cases, it is possible to address this issue by actively cooling the film by blowing in compressed air or the like.

[0049] In the cooling method using rolls, the number of rolls used and the set temperature are not limited, but it is preferable to use multiple rolls for cooling. In the cooling method using rolls, to keep the film temperature in the above range, the roll temperature is preferably 20 to 45°C, and more preferably 30 to 40°C. In the cooling method using rolls, it is preferable to apply a load to the cooling rolls with nip rolls to make the film tightly contacted with the cooling rolls, as this allows for stable cooling.

[0050] Furthermore, in this cooling step, the width shrinkage rate of the film is preferably 0.1 to 20% / min. If the width shrinkage rate is less than 0.1% / min, the suppression of the width shrinkage of the film affects the film tension, which may result in poor film formability and film tearing. If the width shrinkage rate is faster than 20% / min, the effect of suppressing orientation relaxation due to the width shrinkage of the film is small, and the suppression of the bowing phenomenon may be insufficient. It is more preferable that the width shrinkage rate of the film is 0.2 to 18% / min. The width shrinkage rate can be controlled in various ways by setting it based on the cooling step length and film formation speed. Specifically, in the air-cooling method using a tenter, the width shrinkage rate can be set to the desired value by holding both ends with clips and adjusting the rail width.

[0051] The width shrinkage rate of the film in the cooling process shown here is calculated by formula (1) where W1 (mm) is the film width after the width direction stretching process and immediately before entering the cooling process, W2 (mm) is the film width after the cooling process, and T1 (min) is the time it takes to pass through the cooling process. Film width shrinkage rate = (W1-W2) / W1 × 1 / T1 Equation (1) Furthermore, it is preferable that the film be left in a cooled state for a certain period of time in the cooling step (step 3). The reason for this is presumed to be as follows: As mentioned above, it is thought that orientation relaxation occurs during the cooling step when the film is shrunk in width, and it is presumed that a certain period of time is required to stop the orientation relaxation by cooling the film. Therefore, it is presumed that if the cooling step time is insufficient, orientation relaxation cannot be suppressed, and the effect of suppressing the bowing phenomenon is small. When producing the biaxially oriented polyester film of the present invention, the cooling step time is preferably 10 seconds or more, more preferably 15 seconds or more. There is no particular upper limit to the cooling step time, but a time of 60 seconds or less is preferred because it improves productivity.

[0052] (Step 4) Heat treatment of biaxially stretched film The biaxially stretched polyester film obtained in step 3 is heat-treated to obtain a biaxially oriented polyester film. The heat treatment temperature is preferably 180 to 230°C, more preferably 180 to 215°C, and particularly preferably 185 to 210°C. If the heat treatment temperature is less than 180°C, the heat treatment will be insufficient, and it may be difficult to achieve a heat shrinkage rate of 2.5 to 7.0% in the longitudinal direction and 2.5 to 8.0% in the transverse direction after heat treatment at 150°C for 30 minutes. If the heat treatment temperature is higher than 230°C, bowing is likely to occur, making it difficult to control the orientation angle within the above-mentioned ranges, which is undesirable.

[0053] In addition, the heat treatment may be followed by a relaxation treatment if necessary. The relaxation treatment may be carried out in either the width direction or the length direction, and may be carried out simultaneously or separately in the width direction and the length direction. A relaxation rate of preferably 1 to 20%, more preferably 1 to 15%, of the total width of the film is effective for obtaining a film with excellent thermal dimensional stability.

[0054] (Step 5) Manufacturing method of film roll The biaxially oriented polyester film obtained in step 4 is cut using a cutting device equipped with a circular blade that rotates in the same direction as the conveying direction of the transport film to obtain a polyester film roll. The angle of the tangent to the circular blade at the cutting point where the transport film and the circular blade come into contact is preferably 25 degrees or more and 40 degrees or less. If the angle is less than 25 degrees, fluttering of the transport film may occur, causing blade slippage and resulting in poor cutting. Fluttering refers to displacement in a direction perpendicular to the plane of the transport film. If the angle is greater than 40 degrees, the contact area between the end surface of the transport film and the circular blade surface increases, and the resistance of the circular blade to the transport film increases, resulting in poor slitting performance. Because film flutter is significant when the slitting speed increases or decreases, a deeper circular blade depth within the above range is preferred. At a constant speed (when the conveying speed is stable), a shallower circular blade depth within the above range is preferred to reduce resistance when the film comes into contact with the circular blade. At a stable conveying speed, fluttering of the transport film within 10 cm before and after the cutting point is preferably 0.4 mm or less. If the fluttering of the transport film is greater than 0.4 mm, it may cause poor slitting due to blade slippage during slitting, scattering of chips adhering to the slitting blade, or fluctuations in the slitting blade depth, which may result in poor slitting performance. [Example]

[0055] The methods for measuring and evaluating the property values ​​in the examples and comparative examples are as follows.

[0056] (1) Measurement of surface resistivity The film is cut into a size of 110 mm wide and 110 mm long, and left to stand for 24 hours or more under conditions of 23±3°C and 65±10% RH. After that, the surface resistivity is measured according to JIS-C-2151 (2006) using a digital ultra-high resistance meter manufactured by Advantest Corporation.

[0057] (2) Measurement of the amount of foreign matter (amount of chips) adhering to the film surface Figure 1 illustrates the method for measuring the amount of foreign matter adhering to the film surface within a 4 mm widthwise and 1000 m lengthwise range from the outermost edge of a polyester film roll. The center of a low-tack roll (Teknek P-type adhesive roll) was aligned with the outer edge of the polyester film roll. While in contact, the roll was transported 1000 m long using a film transporter to collect foreign matter (chips) adhering to the polyester film roll. The roll was then brought into contact with the center of a 100 mm square transfer sheet (NTT-ATCR dust sampler) so that its center was aligned with the center of the low-tack roll. The roll was then rotated back and forth 100 mm longitudinally on the transfer sheet, transferring the chips collected by the low-tack roll to the transfer sheet. The chips transferred to the transfer sheet were observed using an optical microscope (KEYENCE VHX-7000) within a 16 mm lengthwise and 4 mm widthwise range, based on the horizontal center of the transfer sheet. The observation conditions were a 100x objective lens and automatic area measurement mode. The extraction parameter is set to brightness, and the area is extracted from the image obtained by brightness unevenness removal (strong) + noise removal (medium) with a brightness extraction parameter value of ±0. The detected area (μm 2 ) and the average value A (μm 2 The same measurement was also carried out on the inner surface of the winding, and the average value B (μm 2 ) was calculated. A schematic diagram of the measurement procedure is shown in Figure 1. In this measurement, chips from a 1000m long polyester film roll were transferred to a 100mm square transfer sheet, and an observation area of ​​16mm x 4mm on the transfer sheet was observed. Therefore, the following formula was used to calculate the thickness of 1m of polyester film. 2 Amount of foreign matter adhering per unit (μm 2 / m 2 ) was converted. Amount of attached foreign matter (μm2 / m 2 )=((A+B) / 2×100×10 -3 / 16×10 -3 ) / (1000×4×10 -3 ) (3) Measurement of volume average particle diameter and volume-based particle size distribution in a slurry state Dry powder or dispersion of organic particles was dispersed in a water / ethanol (4 / 1) mixture and air-dried on a sample stage. The particles were then observed at a magnification of 2000x using a scanning electron microscope JSM-6700F (manufactured by JEOL Ltd.). SEM images were taken at 3000 μm. 2 The image was taken as an image, and 200 different fields of view were measured using the image processing software Image-ProPremier (Nippon Roper Co., Ltd.), and aggregated particles were excluded. The volume-based particle size distribution was obtained by plotting the particle size on the horizontal axis and the particle abundance ratio on the vertical axis. The arithmetic mean of the volume-based particle size distribution was taken as the volume-average particle size in the slurry.

[0058] (4) Measurement of volumetric particle size distribution of particles in film A small piece of polyester film was cut perpendicular to the surface using a microtome, and its cross section was observed and photographed at 10,000x magnification using a field emission scanning electron microscope JSM-6700F (manufactured by JEOL Ltd.). The particle size distribution of the particles present in the film was determined from the cross-sectional photograph using image analysis software Image-Pro Plus (Nippon Roper Co., Ltd.). Cross-sectional photographs were selected from different measurement fields, and the diameters (circle equivalent diameters) of 2,500 or more particles randomly selected from the cross-sectional photographs were measured. A volumetric particle size distribution was obtained by plotting particle size on the horizontal axis and particle abundance on the vertical axis. The arithmetic mean of the volumetric particle size distribution was taken as the volume-average particle diameter in the slurry. In the volumetric particle size distribution, the abundance ratio of particles represented by the horizontal axis was calculated using a scale of 10 nm intervals starting from 0 nm, using the formula "abundance ratio = total volume of detected particles with the corresponding particle size / total volume of all detected particles × 100." Furthermore, for example, if the particle diameter has a maximum in the range of more than 110 nm but not exceeding 120 nm, the maximum value is taken to be 0.12 μm, the upper limit of that class. The maximum value of the volume average particle diameter was read from the particle abundance ratio chart obtained above, and the sum of the particle abundance ratio value of the largest maximum value in the volume average particle diameter range of 0.5 μm to 1.2 μm and the particle abundance ratio value of 1.2 μm or more was calculated. A typical example of a volume-based particle size distribution is shown in Figure 2.

[0059] (5) Particle content of each layer The particle content of each layer is calculated from the particle mass contained in a polyester film piece scraped from each layer of the film. The scraped polyester film piece is weighed and designated m1. This is dissolved in 200 mL of a 1 mol / L methanol solution of potassium hydroxide under reflux with a mantle heater set to 100°C for 120 minutes, then cooled and centrifuged. The solvent is evaporated and the resulting solid is weighed and designated m2. When multiple particles are used as a mixture, the solid obtained above can be separated using a density gradient tube. The weighed solid is placed on a sample boat and heated for 45 minutes in a nitrogen atmosphere in a cylindrical electric furnace preheated to 550°C. The sample boat is allowed to cool in a nitrogen atmosphere for 10 minutes, then transferred to a desiccator and allowed to cool to room temperature. The weight is then weighed and designated m3. This trial was performed five times, and the arithmetic average was taken as the content (% by mass). For both organic particles and inorganic particles, if the content was 0.01% by mass or less, it was considered that there was essentially no content, and the particle content of each layer was determined to be the organic particle content of each layer. Organic particle content of each layer (mass%) = (m2−m3) / m1×100 Inorganic particle content of each layer (mass%) = m3 / m1 × 100.

[0060] (6) Film thickness measurement Using a transmission electron microscope (TEM; Hitachi H-600) at an accelerating voltage of 100 kV, the cross section of the film was observed using ultrathin sections (stained with RuO4). The total thickness was determined from the entire cross section, and the layer thickness was measured by measuring the depth from the surface to the deepest point of the particles observed at the interface, i.e., the layer thickness. The magnification can be set appropriately depending on the total thickness and layer thickness of the film being measured, but generally 1000x is appropriate for total thickness measurement, and 10,000 to 100,000x is appropriate for layer thickness measurement.

[0061] (7) Slit blade angle Assuming that the straight line y = 0 (x-axis) is the film pass line, when a circular blade of radius r is set at a depth d relative to the transport film pass line (the center point of the circular blade is on the straight line x = 0 (y-axis)), the circular blade is expressed by Equation 1. The point where Equation 1 and the straight line y = 0 intersect is the cut point where the transport film and the circular blade come into contact, so the slit blade angle was calculated from the angle between the tangent to the circular blade circle (Equation 1) at the point where Equation 1 and y = 0 intersect and the film pass line (y = 0). x 2 +(y-(rd)) 2 =r 2 (Formula 1) (8) Slitting evaluation The slit edge of the polyester film was observed under a scanning electron microscope at 500 to 1000x magnification. Photographs were taken of the images and the presence or absence of streaks of 5µm or more in the thickness direction per 100µm in the machine direction of the slit edge was confirmed. The same confirmation was carried out at 10 different positions, and the number of positions where streaks were confirmed in the thickness direction out of the 10 positions observed was counted to evaluate the slitting properties. Figure 3 shows a schematic diagram of the presence or absence of streaks confirmed in the thickness direction of the slit cross section. ○:0~1 piece △:2~4 pieces ×: 5 or more.

[0062] (9) Film Haze According to JIS K7105 (1981), a sample measuring 4 cm in the longitudinal direction of the film and 3.5 cm in the transverse direction of the film was cut out and measured using a haze meter (HGM-2DP (for C light) manufactured by Suga Test Instruments). Measurements were taken at three points evenly spaced across the film width, and the average value was used as the measurement result.

[0063] (10) Arithmetic mean roughness (Ra) Measurements were made using a three-dimensional microsurface profiler (ET-350K manufactured by Kosaka Laboratory), and the arithmetic mean roughness (Ra) was calculated from the linear profile curve of the film surface in accordance with JIS B0601 (1994). Measurements were made under the following conditions: X-direction measurement length: 0.5 mm, X-direction feed rate: 0.1 mm / sec. Y-direction feed pitch: 5 μm, number of Y-direction lines: 40 Cutoff: 0.25mm. Stylus pressure: 0.02mN. Height (Z direction) magnification: 50,000 times.

[0064] (11) Number of bright spots Bright spot defects refer to light leakage due to defects in film that are detected in crossed Nicols inspection, and the equipment used to evaluate bright spot defects was a crossed Nicols inspection instrument, which was equipped with LED lights (ATTO HBLF-WSL1500, HBLF-WSL700) and a first polarizing plate with an adjustable angle as the lighting means, and a CCD camera (Hyutec GMFMB3B80) with a resolution of 50 μm and a second polarizing plate with an adjustable angle as the light receiving means. 1000 m of film was inspected without changing the detection sensitivity of the camera of the crossed Nicols inspection instrument, and the number of bright spot defects with a detection size of 200 μm or more was counted.

[0065] The number of bright spot defects was evaluated as an index of the ease of inspection in the crossed Nicols inspection (a rating of ○ or higher was considered to be pass). ○: 0.6 bright spots of 200 μm or larger per m 2 The following is the result. △: Bright spots of 200 μm or larger are 0.6 to 1.0 per m 2 is. ×: 1.0 bright spots of 200 μm or larger / m 2 That's all.

[0066] (12) Fluttering of transport film Displacement perpendicular to the plane of the transported film was measured using a laser displacement meter (Keyence LK-G500A). When the width of the intermediate product roll was X, measurements were taken at three points: X / 4, X / 2, and 3X / 4 from the end of the intermediate product roll, 10 cm before and 10 cm after the cut point in the machine direction. After the slitting speed stabilized, displacement perpendicular to the film transport direction was measured at each measurement point for 10 minutes, and the difference between the maximum and minimum measurements was calculated. The largest of the six measured points was taken as the transported film flutter.

[0067] Example 1 A slurry of terephthalic acid and ethylene glycol (ethylene glycol / terephthalic acid molar ratio 1.05 to 1.30) was subjected to an esterification reaction at 255°C while distilling off water. After the esterification reaction was completed, 0.0207% by mass (equivalent to 0.693 mol / t) of diantimony trioxide, 0.014% by mass (equivalent to 0.281 mol / t) of manganese acetate, 0.014% by mass (equivalent to 1.428 mol / t) of phosphoric acid, and 0.0005% by mass (equivalent to 0.09 mol / t) of aqueous potassium hydroxide solution were added to the polyester composition. The mixture was then heated to 290°C under vacuum to carry out a polycondensation reaction, yielding polyester pellets A with an intrinsic viscosity of 0.69.

[0068] Next, an ethylene glycol slurry of divinylbenzene / styrene copolymer crosslinked particles (organic particles) having a volume average diameter of 0.8 μm was added to the above-mentioned polyester pellets A, which were essentially free of particles, using a vented twin-screw kneader to obtain master pellets B, which contained 2.0 mass % of divinylbenzene / styrene copolymer crosslinked particles (organic particles) having a volume average diameter of 0.8 μm relative to the polyester.

[0069] Next, a slurry of terephthalic acid and ethylene glycol (ethylene glycol / terephthalic acid molar ratio 1.05 to 1.30) was subjected to an esterification reaction at 255°C while distilling off water. After the esterification reaction was completed, 0.069 mass% of triethylphosphonoacetate, 0.06 mass% of magnesium acetate, 0.03 mass% of antimony trioxide, 13 mass% of an antistatic agent (sodium dodecylbenzenesulfonate), and 8.4 mass parts of polyethylene glycol (number average molecular weight: 4000) were added to the polyester composition, and the mixture was subsequently heated to 290°C under vacuum to carry out a polycondensation reaction, yielding polyester pellets C containing an antistatic agent with an intrinsic viscosity of 0.62.

[0070] Furthermore, polyester pellets D were obtained, which consisted mainly of recycled film consisting of edge portions generated in the film-forming process of the present invention.

[0071] These polyesters were each dried under reduced pressure at 160°C for 8 hours to a moisture content of 100 ppm. Then, they were fed into separate extruders, melt-extruded at 275°C, filtered through a high-precision filter with a 95% collection efficiency for particles 5 μm or larger, and then laminated together in a rectangular three-layer merging block to form a three-layer laminate consisting of polyester layer A, polyester layer B, and polyester layer A. The resulting laminate was then cast using an electrostatic casting method through a slit die maintained at 285°C, cooled and solidified for 7 seconds on a casting roll with a surface temperature of 25°C, yielding a 570 μm-thick unstretched film. This unstretched film was first stretched 3.4 times in the longitudinal direction while heated using a roll heated to 103°C and a radiation heater. The width shrinkage was 14%. It was then stretched 4.4 times in the transverse direction at 110°C in a tenter. The film was then cooled to a temperature of 35°C at a width shrinkage rate of 18% / min during the cooling process. This cooling process employed a roll system, with the roll temperature at 30°C and the cooling time at 15 seconds. The film was then heat-treated at 195°C, resulting in a three-layer biaxially oriented polyester film with a total film thickness of 38 μm, a film laminate thickness of polyester layer A / polyester layer B / polyester layer A = 1.5 μm / 35 μm / 1.5 μm, and a film width of 5.1 m. This was wound up to produce an intermediate product roll. The resulting intermediate product roll was slit using a cutting device capable of changing the slit blade depth during slitting, resulting in a biaxially oriented polyester film roll with a width of 1300 mm and a length of 6000 m. The slit blade depth was set to satisfy the slit blade angle listed in Tables 1 and 2. The slit blade angle is the angle (°) between the direction of the conveying film and the tangent to the circular blade at the cutting point where the conveying film and the circular blade come into contact. The volumetric particle size distribution, surface resistivity, film haze, arithmetic mean roughness, and amount of foreign matter (amount of chips) adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the extreme edge of the polyester film roll were measured for the obtained biaxially oriented polyester film roll, and the slittability, reflection inspectability, transmission inspectability, and crossed Nicol inspectability were evaluated. The volumetric particle size distribution had a maximum peak of 42% at 1.0 μm, and the proportion of particles 1.2 μm or larger was 21%. The surface resistivity was 1.5 x 10 10 Ω / □, the other side is 1.6×1010 The film haze was 10%, the arithmetic mean roughness was 24 nm, and the amount of chip adhesion was 49.6 μm. 2 / m 2 The slit testability, crossed Nicol testability, reflection testability, and transmission testability all showed good results.

[0072] (Examples 2, 3, 4, and 5), (Comparative Examples 1, 2, 3, and 4) The same procedure as in Example 1 was repeated, except that the amount of polyester master pellet B added to Layer A or the amount of polyester master pellets B and D added to Layer B was varied, to obtain three-layer biaxially oriented polyester films and polyester film rolls. The volume-based particle size distribution, surface resistivity, film haze, arithmetic mean roughness, slitting properties, crossed Nicols inspectability, reflection inspectability, and transmission inspectability were also measured and evaluated using the same methods as in Example 1. In Examples 2, 3, 4, and 5, the slitting properties and each of the inspectability properties were evaluated as ○, which was good. In Comparative Examples 1 and 3, the inspection properties were evaluated as ○, but many streaks were observed on the slit cross section, resulting in a △. In Comparative Example 2, the slitting properties and each of the inspectability properties were evaluated as ○, but the conveyance properties deteriorated. In Comparative Example 4, the slitting properties, crossed Nicols inspectability, and transmission inspectability were all evaluated as ○, but the haze was low and the reflection inspectability was evaluated as ×. The results are summarized in Tables 1 and 2.

[0073] (Examples 6 and 7), (Comparative Examples 5 and 6) The same procedure as in Example 1 was carried out except that the amount of polyester master pellets C added to form layers A and B was changed, thereby obtaining a three-layer biaxially oriented polyester film and a polyester film roll. In Examples 6 and 7, both the slittability and each inspectability were rated as good, with ○. In Comparative Example 5, the slittability and transmission inspectability were rated as good, but the crossed Nicols inspectability was rated fair due to the deterioration of bright spot defects caused by an increase in the amount of attached chips, and the reflection inspectability was rated poor due to low haze. In Comparative Example 6, bright spot defects due to internal foreign matter resulting from the antistatic agent were observed, resulting in the crossed Nicols inspectability being rated fair. The results obtained are summarized in Tables 1 and 2.

[0074] (Examples 8 and 9), (Comparative Examples 7 and 8) The same procedure as in Example 1 was carried out except that the lamination thickness of Layer A and Layer B was changed, and a three-layer biaxially oriented polyester film and polyester film roll were obtained. In Examples 8 and 9, both the slitting property and each inspectability were rated as good, ○. In Comparative Example 7, each inspectability was good, but many streaks were observed on the slit cross section, resulting in a △. In Comparative Example 8, Layer A was thin, and the number of organic particles was reduced, resulting in a decrease in haze and a deterioration in reflection inspectability. In addition, the surface roughness reached a value that could potentially cause a deterioration in conveyability. The results obtained are summarized in Tables 1 and 2.

[0075] (Comparative Example 9) True specific gravity 2.71g / cm 3 Calcium carbonate with a volume average particle size of 1.0 μm was prepared and made into a 10% by mass ethylene glycol slurry. This slurry was dispersed for one hour using a jet agitator and then highly accurately filtered through a filter with a collection efficiency of 95% for particles 5 μm or larger. After the esterification reaction was completed, diantimony trioxide was added to the polyester composition at 0.0105% by mass (equivalent to 0.352 mol / t), manganese acetate at 0.030% by mass (equivalent to 0.602 mol / t), phosphoric acid at 0.008% by mass (equivalent to 0.816 mol / t), and sodium dihydrogen phosphate at 0.010% by mass (equivalent to 0.792 mol / t). Subsequently, a polycondensation reaction was carried out in the same manner as above to obtain polyester master pellets E containing 2.0% by mass of calcium carbonate with a volume average particle size of 1.0 μm and an intrinsic viscosity of 0.62.

[0076] A three-layer biaxially oriented polyester film and polyester film roll were obtained in the same manner as in Example 1, except that the amount of polyester master pellets B added was changed and polyester master pellets E was used as the polyester master pellets constituting Layer A. In Comparative Example 9, the reflection inspectability and transmission inspectability were evaluated as "good", but slit inspectability was evaluated as "poor" because streaks were observed on all slit cross sections observed, and the crossed Nicols inspectability was also evaluated as "poor" because there were many bright spot defects caused by inorganic particles. The results obtained are summarized in Table 2.

[0077] (Comparative Example 10) The same procedure as in Example 1 was carried out, except that pellets F, in which the volume average diameter of the divinylbenzene / styrene copolymer crosslinked particles used in polyester master pellets B was 1.5 μm, were used, to obtain a three-layer biaxially oriented polyester film and a polyester film roll. In Comparative Example 10, although each inspection property was rated as good, streaks were observed on the slit cross section, so the slit property was rated as fair. The obtained results are summarized in Table 2.

[0078] Example 10 The same procedure as in Example 1 was carried out, except that melt extrusion was performed using a rectangular two-layer confluence block for confluence lamination, to obtain a two-layer biaxially oriented polyester film consisting of polyester layer A and polyester layer B, and a polyester film roll. In Example 10, both the slitting property and each inspectability were evaluated as good (○). The results are summarized in Table 1.

[0079] (Comparative Example 11) The same procedure as in Example 1 was carried out to obtain a two-layer biaxially oriented polyester film and polyester film roll, except that melt extrusion was performed using a rectangular two-layer confluence block and the amount of polyester master pellets C added to compose Layer B was changed. In Comparative Example 11, the slitting property and transmission inspectability were good, but the crossed Nicols inspectability was fair due to bright spots caused by chip adhesion, and the reflection inspectability was fair due to low haze. The results are summarized in Table 2.

[0080] (Example 11, Comparative Examples 12 and 13) The same procedure as in Example 1 was carried out, except that the slitting blade angle when slitting the obtained intermediate product roll was changed, to obtain a biaxially oriented polyester film roll consisting of three layers. However, in Comparative Example 13, blade slippage occurred during slitting, resulting in poor cutting, and therefore no biaxially oriented polyester film roll was obtained. In Example 11, both the slitting property and each of the inspectability properties were good, rated ○. In Comparative Example 12, the reflection inspectability and transmission inspectability were rated ○, but the slitting blade was deep even when the slitting speed was stable, which increased the resistance between the slitting blade and the film, resulting in poor slitting property and crossed Nicol inspectability.

[0081] Example 12 A three-layer biaxially oriented polyester film and a polyester film roll were obtained in the same manner as in Example 1, except that the organic particle type used in polyester master pellet B was changed to crosslinked acrylic resin particles. The volume-based particle size distribution, surface resistivity, film haze, arithmetic mean roughness, slitting property, crossed Nicols inspectability, reflection inspectability, and transmission inspectability were also measured and evaluated in the same manner as in Example 1. Both the slitting property and each inspectability were rated as good (○). The results are summarized in Table 1.

[0082] [Table 1]

[0083] [Table 2] [Explanation of symbols]

[0084] 1.Polyester film roll 2. Slightly adhesive roll 3. Transfer sheet 4. Objective Lens 5. Observation range 6. Volumetric Particle Size Distribution of Example 1 7. Volumetric particle size distribution of Comparative Example 1 8. Slit cross section of Example 1 9. Slit cross section of Comparative Example 8 10. Streaks observed in the thickness direction of the slit cross section

Claims

1. A polyester film consisting of two or more layers, having a surface resistivity of 1.0 × 10 ９ Ω / □ or more 1.0×10 １２ A polyester film for use as a release film, having a resistivity of Ω / □ or less, substantially no inorganic particles, a layer having a surface (Layer A) containing organic particles in an amount of 0.75% by mass or more and 1.0% by mass or less, and a layer different from Layer A (Layer B) containing organic particles in an amount of 0.01% by mass or more and 0.1% by mass or less, a haze of 7% or more and 13% or less, and an arithmetic mean roughness of 20 nm or more and 30 nm or less.

2. 2. A polyester film for release films according to claim 1, wherein the thickness of the polyester film is 20 μm or more and 50 μm or less, and the total thickness of the surface layer (layer A) is 1.5 μm or more and 3.5 μm or less.

3. 3. The polyester film for release films according to claim 1, wherein the organic particles have a maximum peak at an abundance ratio of 30% or more at 1.2 μm or less, and an abundance ratio of 30% or less at 1.2 μm or more, in a volume-based particle size distribution plotted with the volume average particle diameter (μm) on the horizontal axis and the particle abundance ratio on the vertical axis.

4. 3. The polyester film for release films according to claim 1, which is used for polarizing plate release films.

5. The polyester film for release films according to claim 3, which is used for polarizing plate release films.

6. 3. A polyester film roll comprising the polyester film according to claim 1 or 2, wherein the amount of foreign matter adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the outermost end of the polyester film roll is 75 μm. ２ / m ２ A polyester film roll for release film, which is as follows:

7. 4. A polyester film roll comprising the polyester film according to claim 3, wherein the amount of foreign matter adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the outermost end of the polyester film roll is 75 μm. ２ / m ２ A polyester film roll for release film, which is as follows:

8. 5. A polyester film roll comprising the polyester film according to claim 4, wherein the amount of foreign matter adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the outermost end of the polyester film roll is 75 μm. ２ / m ２ A polyester film roll for release film, which is as follows:

9. 6. A polyester film roll comprising the polyester film according to claim 5, wherein the amount of foreign matter adhering to the film surface within a range of 4 mm in the width direction and 1000 m in the longitudinal direction from the outermost end of the polyester film roll is 75 μm. ２ / m ２ A polyester film roll for release film, which is as follows:

10. 7. The method for producing a polyester film roll for a release film according to claim 6, further comprising a cutting step of cutting the transport film with a cutting device having a circular blade that rotates in the same direction as the transport direction of the transport film, wherein the depth of the circular blade in the cutting step is different when the transport speed of the transport film increases or decreases and when the transport speed is stable.

11. 11. The method for producing a polyester film roll for use as a release film according to claim 10, wherein the depth of the circular blade in the cutting step is such that the angle of the tangent to the circular blade at the cutting point where the conveying film and the circular blade contact each other is 25 degrees or more and 40 degrees or less.

12. A method for manufacturing a polyester film roll for release film as described in Claim 10, characterized in that when the conveying speed in the cutting process is stable, the fluttering of the conveying film within 10 cm before and after the cut point is 0.4 mm or less.

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