Recycled polyester film

Abstract

To manufacture recycled polyester film that maintains its strength even when using a large amount of recycled polyester raw materials. [Solution] A recycled polyester film containing 40% by mass or more of recycled polyester raw material, wherein the film has a thickness of 1 μm or more and 10 μm or less, and the breaking strength in both the longitudinal and width directions is 230 MPa or more and 350 MPa or less.

Description

【Technical Field】 【0001】 It relates to a recycled polyester film. 【Background Art】 【0002】 Recently, as an international effort, the SDGs Promotion Headquarters has been established as a sustainable development goal, and efforts to recycle resins have been actively carried out as an international goal. In Japan, since around 2000, the Container and Packaging Recycling Law and the Law for the Promotion of Effective Use of Resources have been implemented, and the recycling technology for polyester resins has been almost established. However, in 2022, due to international efforts, the Plastic Resource Recycling Law incorporating the concept of "3R+Renewable" was implemented, and it is trying to shift to a circular economy technology that minimizes the recycling of waste. 【0003】 In the resource recycling of plastics, the recycling of PET bottles mainly composed of polyethylene terephthalate resin, which is representative of polyester, is in the lead. In recent years, the scope of recycling technology has expanded from PET bottles to other industrial materials, such as packaging materials, process materials such as mold release and protection, and functional materials. Also, in recycling methods, there are material recycling (hereinafter sometimes referred to as mechanical recycling) and chemical recycling. Chemical recycling can obtain recycled polyester raw materials comparable to virgin raw materials, but because the number of processes required for recycling increases, the cost and input energy increase, so recycled polyester resins by material recycling are widely adopted. 【0004】 The reuse of material recycling of polyester raw materials once formed is likely to affect the physical properties of recycled products, especially strength. Also, if the recycled products are reused as material recycling again, it is likely to further cause a decrease in physical properties, and the use of the recycled raw materials tends to become negative, and efforts to control the physical properties as recycled raw materials are being studied (for example, Patent Document 1). 【Prior Art Documents】 [Patent Documents] 【0005】 [Patent Document 1] Patent Application No. 2024-100986 [Overview of the project] [Problems that the invention aims to solve] 【0006】 Molded products using recycled polyester raw materials have the problem that when molded into a film, the strength decreases as the thickness decreases. The objective of the present invention is to produce a recycled polyester film in which the strength of the film is maintained even when a large amount of recycled polyester raw materials are used. [Means for solving the problem] 【0007】 To solve the above problems, a preferred embodiment of the present invention has the following configuration. [I] A recycled polyester film containing 40% by mass or more of recycled polyester raw material, wherein the film has a thickness of 1 μm or more and 10 μm or less, and the breaking strength in both the longitudinal and width directions is 230 MPa or more and 350 MPa or less. [II] The recycled polyester film according to [I], wherein the thermal shrinkage rate after heating at least one of the longitudinal and width directions at 150°C for 30 minutes is 3.0% or less. [III] The recycled polyester film according to [I] or [II], wherein the intrinsic viscosity IV of the recycled polyester film is 0.55 dl / g or more and 0.65 dl / g or less. [IV] A recycled polyester film according to any of [I] to [III], wherein the Tmeta of the film observed by differential scanning calorimetry (DSC) is between 195°C and 235°C. [Effects of the Invention] 【0008】 The recycled polyester film of the present invention has excellent strength and allows for the use of large quantities of recycled polyester raw materials. [Modes for carrying out the invention] 【0009】 The polyester film of the present invention will be described in detail below, with specific examples. 【0010】 In the polyester film of the present invention, the polyester is a polyester composed of a dibasic acid and a glycol. As aromatic dibasic acids, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenyletherdicarboxylic acid, diphenylketonedicarboxylic acid, phenylindanedicarboxylic acid, sodium sulfisophthalic acid, dibromoterephthalic acid, and the like can be used. As alicyclic dibasic acids, oxalic acid, succinic acid, adipic acid, azelaic acid, suberic acid, sebacic acid, dimer acid, dodecanedionic acid, cyclohexanedicarboxylic acid, and the like can be used. As glycols, aliphatic diols such as ethylene glycol, propylene glycol, tetramethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, and diethylene glycol can be used; as aromatic diols such as naphthalenediol, 2,2-bis(4-hydroxydiphenyl)propane, 2,2-bis(4-hydroxyethoxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and hydroquinone can be used; and as alicyclic diols such as cyclohexanedimethanol, cyclohexanediol, and spiroglycol can be used. Furthermore, the recycled polyester film of the present invention may contain 40% by mass or more of the recycled polyester raw material described later. Preferably, it is 70% by mass or more, more preferably 80% by mass or more, and more preferably 100% by mass. 【0011】 In particular, polyesters selected from polyethylene terephthalate (PET) and its copolymers, polyethylene naphthalate and its copolymers, polybutylene terephthalate and its copolymers, polybutylene naphthalate and its copolymers, and polyhexamethylene terephthalate and its copolymers are preferably used from the viewpoint of mechanical properties, dimensional stability, and transparency. 【0012】 In the polyester film of the present invention, "film" refers to a sheet-like molded article having the above-mentioned polyester resin as its main component (a component containing more than 50% by mass and up to 100% by mass). Various additives, such as antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, inorganic particles, organic particles, fillers, antistatic agents, and nucleating agents, may be included as minor components in amounts that do not degrade its properties. 【0013】 The particles contained in the polyester film of the present invention are not particularly limited, but both inorganic and organic particles can be used, and two or more types of particles may be used in combination. Examples of inorganic particles include clay, mica, wet and dry silica, colloidal silica, aluminum silicate, calcium carbonate, calcium phosphate, barium sulfate, alumina, alumina silicate, zirconia, talc, montmorillonite, titanium dioxide, carbon black, magnesium stearate, and metal stearate salts such as zinc stearate. As for organic particles, particles composed of resins and compounds such as styrene-based, polyethylene-based, silicone-based, acrylic acid-based, methacrylic acid-based, polyester-based, divinyl compounds, polyimide-based, polyamide-based, "Teflon" (registered trademark)-based, benzoguamine-based, urethane-based, and cellulose-based particles can be used. 【0014】 The polyester film of the present invention preferably has a particle content of 0.3% by mass or less, and may not contain substantially any particles. "Substantially particle-free" means, for example, in the case of inorganic particles, a content that, when inorganic elements are quantified by X-ray fluorescence analysis, is 50 ppm by mass or less (hereinafter simply referred to as ppm), preferably 10 ppm or less, and most preferably below the detection limit. This is because even without actively adding particles to the film, contaminants originating from foreign substances, or dirt adhering to the raw resin or the production lines and equipment in the film manufacturing process, may detach and become mixed into the film. However, from the viewpoint of the film's slipperiness and the ease with which accompanying air escapes when the film is wound into a roll, a particle content of 0.01% by mass or more is more preferable, and the particle content can be appropriately adjusted within a range that does not impair properties such as transparency and surface smoothness. If the particle content exceeds 0.3% by mass, particle aggregation is likely to occur, and coarse protrusions may form on the film surface, which may be undesirable for applications requiring high quality. In the case of the polyester film of the present invention having a laminated structure composed of multiple layers, the particle content of the surface layer is preferably 0.3% by mass or less for the same reasons as described above. 【0015】 The volume-average particle diameter of the particles added to the recycled polyester film of the present invention is preferably 0.01 μm or more and less than 5.0 μm, and more preferably 0.01 μm or more and 3.0 μm or less. If the volume-average particle diameter of the particles is less than 0.01 μm, the film may not exhibit the desired slipperiness. Furthermore, if the volume-average particle diameter exceeds 5.0 μm, the accuracy of the filtration filter for the molten resin must be reduced, which lowers the efficiency of collecting foreign matter. In addition, the protrusions of coarse particles on the film surface themselves can cause thickness unevenness, which may be undesirable in use. 【0016】 One method for obtaining a polyester resin containing particles is to disperse the particles in a predetermined proportion in a slurry form in ethylene glycol, which is a diol component, and add this ethylene glycol slurry at any stage before the polymerization of the polyester resin is completed. Furthermore, to improve the dispersibility of particles in a polyester resin containing particles, it is effective to lower the particle concentration in the resin or to add the aqueous sol or alcohol sol obtained during particle synthesis without drying it first. 【0017】 Furthermore, the recycled polyester film of the present invention may be a single layer or a laminated structure of two or more layers. The recycled film of the present invention is preferable because it is easy to use a timely mixture of recovered polyester resin from film edge scraps held by clips in the stretching process, film scraps generated from the start of film formation until product sampling, film roll scraps that failed product inspection, and / or recycled polyester resin from used film, as long as it does not adversely affect the properties of the film surface. The particle content in the surface layer can be kept to 0.3% by mass or less, while also containing recovered polyester resin and / or recycled polyester resin in the outermost layer, so as not to form coarse protrusions on the film surface. 【0018】 The recovered polyester resin generated in the film manufacturing process can be recycled by methods described in Japanese Patent Publication No. 2016-175066, which involve crushing flakes with a crusher, compressing and cutting them in a granulator to form pellets (for example, cylindrical molded products with a height of 30 mm or less), or by melt-kneading the crushed flakes in an extruder, filtering out coarse particles and foreign matter with a filter, extruding them in strand form from a die, and cutting them while cooling to form chips. These recycled materials can be mixed with virgin polyester resin in a timely manner. However, because these recovered polyester resins have undergone thermal history and become low-molecular-weight, it is unavoidable that both the IV and shear viscosity will decrease each time the recovered polyester resin is repeatedly used in film manufacturing with a 100% self-recycling rate. However, by adding virgin polyester resin and / or recycled polyester resin from used film, as described later, and adjusting the content of each resin relative to the total mass of polyester resin constituting the film, it is possible to manufacture polyester films with IV and shear viscosity within a desirable range. 【0019】 Therefore, while it is preferable to increase the content of recovered polyester resin in the polyester resin that constitutes the film from the viewpoint of cost reduction and reduction of environmental impact, the upper limit of the content should be determined within a range that does not impair the required characteristics for each film application, such as thickness uniformity, mechanical properties, dimensional stability, transparency, and surface smoothness. 【0020】 Furthermore, the present invention allows for the provision of a smooth-slip layer, an adhesive layer, a release layer, a functional layer, etc., on the surface layer of the polyester film. The smooth-slip layer may be made by adding a certain amount of inorganic particles or organic particles as particles to a water-soluble resin; the adhesive layer may be made by adding functional groups to a water-soluble resin; the release layer may be made of a silicone release functional resin or a silicone-free release functional resin; and the functional layer may be made of a hard-coat curable resin, a thermoplastic resin or curable resin that utilizes refraction. 【0021】 The method of forming a lubricious layer, an adhesive layer, a release layer, a functional layer, etc. on the surface of a polyester film is not particularly limited as long as the effects of the present invention are not impaired. For example, a co-extrusion method, a coating method, a dry lamination method, a melt lamination method, etc. can be used. Among them, since the procedure is simple, it is preferable to use the coating method. As the method of applying the coating agent, methods such as a roll coater, a gravure coater, a bar coater, etc. can be used. The coating process can be appropriately selected, such as before the stretching of the polyester film, during the stretching process, or after the stretching and heat treatment are performed. 【0022】 The intrinsic viscosity IV of the recycled polyester film of the present invention is preferably 0.55 dl / g or more and 0.65 dl / g or less. When the intrinsic viscosity IV of the film is less than 0.55 dl / g, the strength is low because the molecular weight is small, and when the film thickness is thin, the breaking strength of the film tends to decrease. Also, the rheometer viscosity ηH at 280°C and a shear rate of 31.4 rad / s, which will be described later, also tends to deviate from the preferable range of the present invention. On the other hand, when the intrinsic viscosity IV of the film exceeds 0.65 dl / g, the breaking strength tends to be high because the molecular weight is large, but varieties with a thin film thickness tend to break easily during the film forming process, especially during stretching. Considering further recycling the recycled polyester film of the present invention, it is significant to set the intrinsic viscosity IV of the already formed film to 0.65 dl / g or less. Preferably, the intrinsic viscosity IV of the film is 0.58 dl / g or more and 0.63 dl / g or less. 【0023】 The virgin polyester resin constituting the polyester film of the present invention can be produced by a known method. For example, in the case of PET, the esterification process is carried out under stirring using one or more esterification reaction tanks. For example, when using a single esterification reaction tank, the reaction temperature is usually 240°C or more and 280°C or less, the relative pressure to atmospheric pressure is usually 0 kPa or more and 400 kPa or less, and the reaction time is usually 1 hour or more and 10 hours or less. The esterification reaction rate of the esterification reaction product obtained in the esterification process is usually 95% or more. 【0024】 The melt polycondensation process 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 atmospheric pressure and distilling ethylene glycol generated under heating and stirring out of the system. For example, in the case of a batch process using a single polycondensation reaction vessel, the reaction temperature is usually 250°C or higher and 290°C or lower, the final absolute pressure after gradually reducing the pressure from atmospheric pressure is usually 1.3 kPa or lower and 0.013 kPa or higher (10 Torr or lower and 0.1 Torr or higher), and the reaction time is usually 1 hour or longer and 20 hours or shorter. 【0025】 The intrinsic viscosity (IV) and shear viscosity of the virgin polyester resin can be determined by the stirring torque of the polymer at the end of polymerization. When the stirring torque is high, the IV of the polymer is high and the shear viscosity is also high. The end-point determination stirring torque of the polymerization apparatus may be set so as to achieve the target IV and shear viscosity. In order to obtain the polyester film of the present invention, it is preferable to set the end-point determination stirring torque so that the IV and shear viscosity of the virgin polyester resin as the raw material are slightly higher than the IV and shear viscosity of the film. Generally, the increasing and decreasing tendencies of IV and shear viscosity are the same, but depending on the type of additive and its addition amount, even if the target shear viscosity is achieved, the IV may change. 【0026】 The obtained virgin polyester resin after the completion of polymerization may be discharged in a strand shape from the lower part of the polymerization apparatus and cut by a cutter while being water-cooled. Since the chip shape can be controlled by cutting, a virgin polyester resin having a preferable bulk density in the present invention can be obtained. 【0027】 The polycondensation reaction catalyst used in the present invention can be one or more of the following: antimony trioxide, antimony pentoxide, antimony acetate, antimony glycolate, germanium dioxide, organotitanium compounds, etc. When using an antimony compound and / or a germanium compound, the sum of the antimony and germanium content relative to the total mass of the polyester resin constituting the film is preferably 20 ppm to 200 ppm from the viewpoint of polycondensation reactivity and solid-phase polymerization reactivity, and more preferably 50 ppm to 150 ppm from the viewpoint of heat resistance and hydrolysis resistance. If it exceeds 200 ppm, although the polycondensation reactivity and solid-phase polymerization reactivity improve, the decomposition reaction during remelting is also promoted, which increases the carboxyl terminal groups, causing a decrease in heat resistance and hydrolysis resistance, and may also cause the formation of foreign matter due to aggregation. 【0028】 The recycled polyester film of the present invention may also contain one or more additives such as metal compounds including manganese, magnesium, calcium, and cobalt, or alkali metal salts, alkaline earth metal salts, silicone compounds, for example, lithium acetate, sodium acetate, potassium acetate, potassium hydroxide, magnesium acetate, magnesium hydroxide, magnesium alkoxide, magnesium carbonate, potassium hydroxide, calcium hydroxide, calcium acetate, calcium carbonate, manganese oxide, manganese acetate, polydimethylsiloxane, polydiethylsiloxane, polymethylphenylsiloxane, polyorganosiloxane, and reactive silicones having functional groups that react with the organic groups of the polyester resin at both or one end. When using magnesium compounds and / or manganese compounds, the sum of the magnesium and manganese content relative to the total mass of the polyester resin constituting the film is preferably 10 ppm to 150 ppm, and more preferably 30 ppm to 130 ppm. From the viewpoint of improving electrostatic application for adhering the sheet-like molten resin to the casting drum and suppressing thermal decomposition, the content is preferably 10 ppm or more, and from the viewpoint of suppressing foreign matter due to aggregation of metal compounds, it is preferably 150 ppm or less. When using a silicone-based compound, the content of silicon element relative to the total mass of the polyester resin constituting the film is preferably 5 ppm to 100 ppm. This silicon element is an element derived from the silicone compound. From the viewpoint of promoting a decrease in shear viscosity, it is preferably 5 ppm or more, and from the viewpoint of suppressing the bleed-out of the silicone compound when the film is used, it is preferably 100 ppm or less. By including silicone, which is commonly used as a mold release agent, in the polyester resin, the wall slipperiness in the molten state, i.e., fluidity is improved, and the shear viscosity can be reduced. From the viewpoint of maintaining intrinsic viscosity, it is preferable to use a silicone compound with a weight-average molecular weight close to that of polyester. For example, if the polyester is PET, it is preferable to use a silicone compound with a weight-average molecular weight of 30,000 to 50,000.For example, the method described in Japanese Patent Publication No. 2007-146049 can be used to adjust the weight-average molecular weight of a silicone compound. 【0029】 The recycled polyester film of the present invention may use phosphorus compounds as stabilizers, such as phosphoric acid, trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, dibutyl phosphate, monobutyl phosphate, triethyl phosphate, triethyl phosphate noacetate, tris(triethylene glycol) phosphate, phosphorous acid, dioctyl phosphate, triphenyl phosphate, trisdodecyl phosphate, trisnonylphenyl phosphate, methyl acid phosphate, ethyl acid phosphate, triethylene glycol acid phosphate, isopropyl acid phosphate, butyl acid phosphate, etc. The phosphorus content relative to the total mass of the polyester resin constituting the film is preferably 5 ppm to 100 ppm, and more preferably 5 ppm to 50 ppm. This content prevents foreign matter formation and a decrease in polymerization activity due to the phosphorus compounds. ppm is based on mass. 【0030】 In the present invention, in order to suppress the amount of terephthalic acid generated by the decomposition reaction of the polymer when the film is heated after melt-forming, it is preferable to include an alkali metal phosphate in addition to the phosphorus compound that is generally added during polyester polymerization. This improves hydrolysis resistance and thermal decomposition resistance, suppresses the amount of terephthalic acid generated when the film is heat-treated or heat-processed, and allows for the maintenance of a more suitable terephthalic acid concentration. From the viewpoint of the amount of oligomers generated when the film is heated or heat-processed, the alkali metal element content relative to the total mass of the polyester resin constituting the film is preferably 5 ppm to 50 ppm, and more preferably 10 ppm to 40 ppm. 【0031】 The alkali metal phosphate salts used in this invention are not particularly limited, but include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, and trilithium phosphate. Among these, sodium dihydrogen phosphate and potassium dihydrogen phosphate are preferred from the viewpoint of hydrolysis resistance. 【0032】 The recycled polyester film of the present invention may contain recycled polyester resin from used films or PET bottles. From the viewpoint of reducing environmental impact, it is preferable to determine the upper limit of the content within a range that does not impair the required characteristics for each film application, such as thickness uniformity, mechanical properties, dimensional stability, transparency, and surface smoothness. The recycled polyester resin may contain the same polycondensation reaction catalyst, additives, stabilizers, and alkali metal phosphates as the virgin polyester resin described above. 【0033】 Used film refers to film that has been used as a product for a specific purpose. As a result of being used as a product for a specific purpose, the performance of the product is lost, and by recycling the film that would otherwise be discarded, it is possible to reduce the environmental burden. Examples of used film include hard coat layers, refractive adjustment layers, and easy-adhesion layers that facilitate bonding with other materials, which are representative of the functional layers of optical films, and in the case of release films, the base material of adhesive tape, the release paper of adhesive tape, and films used in product manufacturing processes. Among these, films used in product manufacturing processes, especially release films used in the manufacturing processes of multilayer ceramic capacitors and polarizing films, have seen an increase in usage in recent years, so recycling them is preferable because it reduces the amount of waste and leads to a reduction in the environmental burden. When the used film is a release film used in the manufacturing process of multilayer ceramic capacitors, impurities contained in the composition may include barium titanate, a component of the material being released, and silicone, a component of the release agent. When obtaining a film from recycled polyester resin of used film containing a large amount of such release agent components and mold release material components, a problem arises in the generation of a large amount of foreign matter. Therefore, it is preferable to remove the sum of the content of impurity elements such as barium and titanium elements, excluding silicon elements derived from silicone, from the total recycled polyester resin to 10 ppm or less, and more preferably to 5 ppm or less. The content of silicon elements derived from silicone is preferably 5 ppm or more for the effect to manifest when promoting the reduction of the shear viscosity of the recycled polyester resin, and is preferably 100 ppm or less from the viewpoint of suppressing the bleed-out of silicone compounds when the film is used. 【0034】 Two methods are known for recycling used film and PET bottles: chemical recycling and mechanical recycling. Chemical recycling involves chemically decomposing used film back into crude raw materials (monomers) and then repolymerizing polyester. This method can produce recycled polyester resin that is indistinguishable from virgin polyester resin, but it has the drawback of being a longer process and more expensive than producing virgin polyester resin. Mechanical recycling, for example, is described in Japanese Patent Publication No. 2023-81479. This method involves removing the coating (impurities) from the surface of used film crushed into flakes using an alkaline aqueous solution, and then washing with water to remove any remaining coating residue and alkaline components. Next, the material is dried to evaporate the moisture, melted and kneaded in an extruder, filtered to separate coarse particles and foreign matter, then extruded from a die in a strand shape, and cut while cooling to form chips. This method allows for the production of recycled polyester resin at a lower cost than chemical recycling. Alternatively, recycled polyester resin can be obtained by unwinding film from used film rolls using the method described in Japanese Patent Publication No. 2023-142608, removing the coating while transporting the film roll-to-roll through a tank of water containing a cleaning solution, drying, crushing, and then following the same procedure for the chipping process. Furthermore, if the coating of the used film contains a silicone compound, the content of silicon elements derived from silicone in the overall recycled polyester resin can be adjusted by controlling the alkali concentration, temperature, and processing time of the alkaline aqueous solution used. Therefore, when using recycled polyester resin in the polyester film of the present invention, while not particularly limited, mechanically recycled recycled polyester resin is more preferably used. 【0035】 Examples of alkaline aqueous solutions used in mechanical recycling include lithium hydroxide, sodium hydroxide, and potassium hydroxide aqueous solutions, from the viewpoint of improving the peelability of the coating, with sodium hydroxide being preferred. 【0036】 The concentration of the alkaline aqueous solution used is preferably between 0.5% by mass and 6.0% by mass. Below 0.5% by mass, the peelability of the coating decreases, and peeling may take a long time. Above 6.0% by mass, hydrolysis is accelerated, which may cause a decrease in the molecular weight and IV of the polyester support. 【0037】 It is preferable that the alkaline aqueous solution contains a surfactant. The surfactant content is preferably 0.01% by mass or more and 0.10% by mass or less of the total amount of the alkaline aqueous solution. Adding a surfactant increases the penetration of the alkaline aqueous solution into the interface between the polyester support and the coating, thereby promoting peeling and suppressing re-adhesion between the peeled coating and the polyester support. Examples of surfactants include nonionic surfactants, anionic surfactants, and cationic surfactants, with nonionic and anionic surfactants being preferred. Examples of nonionic surfactants include polyethylene glycol ether-based surfactants, particularly polyethylene glycol ethers of higher alcohols and polyethylene glycol ethers of alkylphenols. Examples of anionic surfactants include alkylbenzene sulfonates and alkyl sulfate esters. To prevent the precipitation of surfactants in the alkaline aqueous solution and the re-adhesion of impurities insoluble in alkali, it is preferable to perform stirring and washing in a washing tank equipped with stirring blades. 【0038】 The temperature of the alkaline aqueous solution is preferably between 60°C and 98°C. Below 60°C, the peelability of the coating laminated on the polyester support decreases, and peeling may take a long time. Above 98°C, the temperature is close to the boiling point, requiring a pressurized washing tank, and may cause hydrolysis or dissolution of the polyester support due to heating. 【0039】 The processing time by stirring and washing is preferably 15 minutes to 30 minutes when the washing concentration is 10% by mass or less (9 or more parts by mass of alkaline aqueous solution containing surfactant relative to 1 part by mass of the material being washed). By setting the time within this range, the coating can be efficiently removed from the polyester support. 【0040】 After washing with an alkaline aqueous solution, it is preferable to rinse with water. Water rinsing removes any trace residue of the coating remaining on the polyester support and removes any adhering alkaline components. Similar to alkaline washing, a washing tank equipped with agitators can be used. From the viewpoint of washing time and cost, it is preferable to perform the process in one stage. Furthermore, for both alkaline washing and water rinsing, the stirring speed should be in the range of 100 rpm to 300 rpm, and the processing time by stirring and washing should be 15 minutes to 30 minutes. By setting the above range, the coating can be efficiently removed from the polyester support. After water rinsing, it is preferable to vacuum dry at 60°C to 200°C. More preferably, it should be 90°C to 120°C. 【0041】 A recycled polyester resin can be obtained by melting and kneading a dried polyester support in an extruder, filtering out coarse particles and foreign matter, extruding it in strand form from a die, and cutting it while cooling. When the coating of the used film contains a silicone compound, a recycled polyester resin intentionally containing silicon elements derived from the silicone in a concentration of 5 ppm to 100 ppm can be obtained within the above-mentioned range of alkaline aqueous solution concentration, temperature, and processing time. 【0042】 The thickness of the recycled polyester film of the present invention is preferably 1 to 10 μm. More preferably, it is 2 μm to 8 μm. If the thickness is less than 1 μm, the thickness is too thin, and it becomes necessary to limit the amount of recycled polyester raw material used in the recycled polyester of the present invention. On the other hand, if the thickness exceeds 10 μm, a large amount of recycled polyester raw material can be used, but it becomes difficult to control thickness unevenness, so in the present invention, a thickness of 10 μm or less is preferred. As a method for adjusting the film thickness to 1 μm or more and 10 μm or less, the thickness of the film after biaxial stretching can be measured with a non-contact thickness gauge, and the amount of polymer discharged from the T-die can be controlled to achieve the target thickness. 【0043】 Preferably, the longitudinal and widthwise breaking strengths of the recycled polyester film of the present invention are 230 MPa or more and 350 MPa or less. The longitudinal direction refers to the direction of progress in the film manufacturing process, and the widthwise direction refers to the direction perpendicular to the longitudinal direction within the plane. A longitudinal breaking strength of 230 MPa or more can suppress film breakage during the processing process, and given the thickness of the recycled film of the present invention, the limit is 350 MPa or less due to the size of the manufacturing facility site. More preferably, it is 250 MPa or more and 350 MPa or less. Depending on the type of recycled polyester raw material, using a large amount of recycled polyester raw material tends to decrease the breaking strength. In the present invention, the breaking strength of the final film can be adjusted by controlling the rheometer viscosity ηH of the recycled polyester raw material and the film manufacturing process, particularly the heat-fixing temperature. 【0044】 Furthermore, the recycled polyester film of the present invention has a breaking strength in the width direction of 230 MPa to 350 MPa. By keeping it within this range, the breaking strength in both the longitudinal and width directions can be increased, resulting in excellent isotropy of the film's breaking strength. More preferably, it is between 250 MPa and 300 MPa. In particular, in the width direction, due to the limitations of the rail width in the width direction of the manufacturing process described later, the limit is 350 MPa or less. 【0045】 The recycled polyester film of the present invention preferably has a thermal shrinkage rate of 3.0% or less in at least one of the longitudinal and width directions after heating at 150°C for 30 minutes. More preferably, it is 2.0% or less, and more preferably 1.0% or less. By reducing the thermal shrinkage rate, dimensional stability during processing can be improved. This range of thermal shrinkage rate can be more easily achieved by adjusting the intrinsic viscosity and rheometer viscosity ηH of the recycled polyester raw materials, the amount of these recycled polyester raw materials blended, or by adjusting the heat-fixing temperature in the film manufacturing process described later. 【0046】 It is preferable that the Tmeta (hereinafter sometimes simply referred to as Tmeta) of the recycled polyester film of the present invention, as observed by differential scanning calorimetry (DSC), is between 195°C and 235°C. Being within this range makes it easier to satisfy the film's breaking strength requirement. If Tmeta is below 195°C, the amount of amorphous components in the film increases, and the film's breaking strength tends to increase. On the other hand, if Tmeta exceeds 235°C, the amorphous components crystallize, improving the dimensional stability of the film during heating, but the breaking strength tends to decrease. 【0047】 Next, the method for producing the polyester film of the present invention will be described, but the present invention is not limited to such examples. 【0048】 Virgin polyester resin, recovered polyester resin, and recycled polyester resin are mixed in predetermined proportions, dried, and then supplied to a known extruder. In the production of the polyester film of the present invention, single-screw or twin-screw extruders can be used. In addition, a vented extruder equipped with a vacuum line can be used to eliminate the drying process of the polyester resin. When producing a film with two or more layers, a tandem extruder can be used for the layer with the largest extrusion volume, in which the function of melting the polyester resin and the function of maintaining the molten resin at a constant temperature are divided between the extruders. A tandem extruder is preferable as a process to reduce thickness unevenness because it stabilizes the temperature of the molten resin at high extrusion levels, thereby reducing viscosity variations of the molten resin. When the melting point of the polyester resin is Tm, the melting temperature is preferably between Tm and Tm+45°C. Below Tm, the resin will not melt, and above Tm+45°C, the resin will decompose and deteriorate, which may cause a significant decrease in IV and shear viscosity. Furthermore, the resin may not be uniformly heated by the time it reaches the T-die, which may affect thickness unevenness. 【0049】 The molten resin discharged from the extruder is filtered. Since even very small foreign matter can become large protrusions if it enters the film, it is effective to use a filter with high collection efficiency that captures 95% or more of foreign matter larger than 5 μm. On the other hand, if the collection efficiency of the filter is too high, the degree of pressure increase may increase, so using a filter with even higher collection efficiency that captures 95% or more of foreign matter smaller than 5 μm may be an undesirable embodiment in terms of suppressing thickness unevenness. Next, the molten resin is extruded from the T-die into a sheet and cooled and solidified on a casting drum to obtain an unstretched film. It is desirable to be able to feed back the film thickness after stretching the unstretched film in the longitudinal and width directions into the lip gap of the T-die in order to suppress thickness unevenness. In addition, it is desirable to surface treat the lip of the T-die with tungsten carbide and reduce the corner radius of the lip tip in order to suppress streaks that adhere to and grow on the lip. The sheet extruded from the T-die is cooled on a casting drum to make an unstretched film. In this case, installing a static mixer and a gear pump in the flow path of the molten resin is an effective means of suppressing longitudinal thickness unevenness in the present invention, from the viewpoint of stabilizing back pressure and suppressing thickness fluctuations. The gear pump is important for uniformly controlling the longitudinal thickness because it has the function of blocking pressure fluctuations in the extrusion process, and longitudinal thickness unevenness can be kept to a minimum by keeping the rotation speed of the gear built into the gear pump constant. 【0050】 Regarding the rotational accuracy of the casting drum, eccentricity of the casting drum can cause speed fluctuations and surface irregularities on the casting drum surface, which can affect thickness unevenness in the longitudinal direction. Since speed fluctuations on the casting drum surface significantly affect thickness unevenness in the longitudinal direction, it is a preferred embodiment to suppress eccentricity by attaching balance weights to arbitrary points on the circumference of the casting drum end face to reduce this effect. Furthermore, using two motors to rotate the casting drum, separating their functions into drive and brake, is also a preferred embodiment for suppressing thickness unevenness in the longitudinal direction. 【0051】 The unstretched film that has landed on the casting drum is brought into contact with the drum using electrostatic force with a pinning device. The pinning device applies an electric charge to the casting drum from an electrostatically applied wire or tape across the entire width of the unstretched film, and the film and the casting drum are brought into contact by the electrostatic charge at the interface between the casting drum and the film. In this case, in order to keep the charge strength constant in the width direction, it is preferable that the distance from the electrostatically applied wire or tape to the film be equal across the entire width of the unstretched film. Furthermore, in order to maintain an appropriate level of contact between the casting drum and the film, it is preferable to adjust the strength of the electrostatically applied current, and it is preferable to use the electrostatically applied wire or tape while winding it in one direction, as it may be contaminated with oligomers generated from the unstretched film. The film that has been brought into contact with the casting drum and cooled is peeled off the casting drum using a separation roll and guided to the next stretching process. In this case, water may be passed through the separation roll for film cooling, or the separation roll may be driven. 【0052】 Subsequently, the unstretched film is stretched biaxially in the longitudinal and width directions, and then heat-treated. The stretching process may be simultaneous biaxial stretching or sequential biaxial stretching. Simultaneous biaxial stretching is preferable as a stretching method because it does not involve stretching by rolls, thus avoiding localized heating of the film surface and uneven stretching due to uneven roll rotation, making it easier to control thickness variations. 【0053】 In simultaneous biaxial stretching, the widthwise ends of the unstretched film are gripped by clips on each side of the tenter device, and after preheating the unstretched film by applying hot air, it is stretched simultaneously in the longitudinal and widthwise directions, with a stretching temperature of Tg or higher and Tg+140°C or lower, more preferably Tg or higher and Tg+70°C or lower, where Tg is the glass transition temperature of the polyester resin. Setting the stretching temperature to Tg or higher is preferable in that it can suppress film breakage, and setting the stretching temperature to Tg+140°C or lower is preferable in that sufficient strength can be obtained. Furthermore, from the viewpoint of reducing stretching unevenness, the total stretching ratio (area stretching ratio) in the longitudinal and widthwise directions is preferably set to, for example, 8 times or more and 30 times or less. Setting the area stretching ratio to 8 times or higher allows for good thickness uniformity and sufficient strength, and setting it to 30 times or less reduces film breakage during the manufacturing process. 【0054】 Subsequently, assuming the melting point of the polyester resin is Tm, heat setting is performed at a temperature between Tm-80°C and Tm-20°C for, for example, 0.5 seconds to 20 seconds. By setting the heat setting temperature above Tm-80°C, crystallization of the film can be promoted, stabilizing the structure. Furthermore, by setting the heat setting temperature below Tm-20°C, the decrease in Young's modulus due to the relaxation of the amorphous chain portion of the polyester can be suppressed, thereby obtaining sufficient strength. After that, in order to adjust the dimensional change rate and flatness, a relaxation treatment may be performed in the longitudinal and / or widthwise directions at, for example, 50°C or higher and below the heat setting temperature, for, for example, 0% to 10%, during the heat treatment or in the intermediate cooling zone or slow cooling zone thereafter. In this case, it is preferable to control the temperature difference in the widthwise direction inside the oven to within 5°C in order to ensure good thickness uniformity in the widthwise direction. 【0055】 Next, the case of sequential biaxial stretching will be explained. First, longitudinal stretching is usually performed by the difference in peripheral speed of the rolls, and this stretching may be performed in one stage or in multiple stages using multiple pairs of rolls. When performing stretching in multiple stages, it is preferable to set the stretching ratio in one stretching section to 3 times or less in order to ensure appropriate stretching tension. To reduce thickness unevenness in the longitudinal direction, a drive system in which the peripheral speed of the rolls can be set individually for each roll is preferred. In the longitudinal stretching process, the material of the conveying rolls is selected by either heating the unstretched film to above Tg before stretching, or conveying it to the stretching zone while maintaining a temperature below Tg and then heating it all at once using a heater during stretching. The stretching ratio is preferably 2 times or more and 7 times or less, particularly preferably 3 times or more and 6 times or less, and the stretching temperature is preferably, for example, above Tg and 60°C or less. 【0056】 Next, the film is transported while gripping both ends in the width direction with clips on a tenter device, and after preheating the film to above Tg by applying heat, it is stretched in the width direction. The stretching ratio is, for example, 2 to 7 times, particularly preferably 3 to 6 times, and the stretching temperature is, for example, above Tg or below Tg+140°C, particularly preferably above Tg or below T+70°C. Furthermore, in order to mitigate bowing that occurs in the transverse stretching process, re-longitudinal stretching and / or re-transverse stretching may be performed, which can reduce the occurrence of thickness unevenness due to local deformation. The subsequent process from heat setting to slow cooling is the same as for simultaneous biaxial stretching. 【0057】 After biaxial stretching, the film is cooled in the transport process, then the edges are cut and the film is wound up to obtain an intermediate roll. In this transport process, the film thickness in the width direction is measured, and this data is used as feedback to adjust the film thickness by adjusting the T-die thickness, etc., and foreign matter can be detected by a defect detector. Thickness can be measured using beta rays, X-rays, or optical interferometry. Measurement can be performed by moving a single measuring device traversing in the width direction to measure the thickness of the entire width, or by moving multiple measuring devices traversing within sections divided in the width direction to measure the thickness of the entire width, or, in inspection equipment with a wide measurement range, by fixing multiple measuring devices in the width direction to measure the thickness of the entire width. Furthermore, in the film manufacturing process, measurement is preferably performed within the transport process described above. Note that thickness measurement can also be performed in the transport process of the slitter and rewinder after unwinding the film from the intermediate roll. [Examples] 【0058】 The present invention will be described in more detail below based on comparative examples and embodiments. However, the present invention is not limited to the embodiments described below. 【0059】 [Method for evaluating physical properties] (1) Intrinsic viscosity of the film IV (dl / g) A polyester resin or polyester film was dissolved in 100 mL of orthochlorophenol (solution concentration C = 1.2 g / mL), and the viscosity of the solution at 25°C was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was also measured. Using the obtained solution viscosity and solvent viscosity, [η] was calculated using the following formula (B), and the resulting value was defined as the intrinsic viscosity IV. ηsp / C = [η] + K[η] 2 ·C ···Formula (B) (Here, ηsp = (solution viscosity / solvent viscosity) - 1, and K is the Huggins constant (assumed to be 0.343).) If there are insoluble substances in the solution in which the polyester resin or polyester film is dissolved, the solution is filtered and the mass of the filtered material is measured. The mass of the sample to be measured is obtained by subtracting the mass of the filtered material from the mass of the sample to be measured. 【0060】 (2) Rheometer viscosity ηH (Pa·s) A polyester resin sample or a polyester film sample cut into 40 mm squares and stacked was prepared. It was dried in a vacuum dryer at 150°C for 8 hours until immediately before measurement. After returning to atmospheric pressure with nitrogen, 0.4 g was immediately weighed. Next, 0.4 g of the sample was packed into a parallel plate (60 mm diameter) of a RHEOSOL-G3000 rheometer (manufactured by UBM Co., Ltd.). The distance between the upper and lower plates was set to 5 mm, and the plate was melted at 280°C for 1 minute under a nitrogen atmosphere. Then, the plate distance was adjusted to 0.5 mm, and the shear viscosity ηH was measured at a shear rate of 31.4 rad / s. ηH was calculated as the arithmetic mean of two measurement results, rounded to three decimal places. 【0061】 (3) The minute endothermic peak temperature Tmeta (°C) determined by differential scanning calorimetry (DSC) The minute endothermic peak temperature Tmeta(°C) was measured using a differential scanning calorimetry system "Robot DSC-RDC220" manufactured by Seiko Electronics Industries, Ltd., in accordance with JIS K7122-1987 (referencing the 1999 edition of the JIS Handbook), and the disk session "SSC / 5200" was used for data analysis. 5 mg of film was weighed into a sample pan, and the temperature was increased from 25°C to 300°C at a heating rate of 20°C / min for measurement. Tmeta(°C) was defined as the minute endothermic peak temperature before the crystal melting peak in the obtained differential scanning calorimetry chart. If the minute endothermic peak was difficult to observe, the area around the peak was magnified in the data analysis unit to read the peak. 【0062】 Although the method for reading the graph of minute endothermic peaks is not described in JIS, it was performed based on the following method. First, a straight line was drawn between the values ​​of 135°C and 155°C, and the area on the endothermic side of the curve on the graph was calculated. Similarly, the area was calculated for 17 points: 140°C and 160°C, 145°C and 165°C, 150°C and 170°C, 155°C and 175°C, 160°C and 180°C, 165°C and 185°C, 170°C and 190°C, 175°C and 195°C, 180°C and 200°C, 185°C and 205°C, 190°C and 210°C, 195°C and 215°C, 200°C and 220°C, 205°C and 225°C, 210°C and 230°C, 215°C and 235°C, and 220°C and 240°C. Since the endothermic amount of minute peaks is usually between 0.2 and 5.0 J / g, only data with an area between 0.2 J / g and 5.0 J / g will be treated as valid data. From a total of 18 area data points, Tmeta(°C) will be defined as the peak temperature of the endothermic peak in the temperature range of the data point that is valid and shows the largest area. If there is no valid data, Tmeta(°C) will be considered as none. 【0063】 (4) Film thickness (μm) The film was measured using the micrometer method (JIS-C-2151 (2019)). If the thickness was 50 μm or less, 10 sheets were stacked and measured, and the thickness per sheet was obtained by dividing by the number of sheets and rounding to one decimal place. 【0064】 (5) Breaking strength (MPa) Using the "Tensilon" tensile testing machine (registered trademark), measurements were taken with a tensile speed of 300 mm / min, a width of 10 mm, and a sample length of 100 mm. The number of measurements was n=5, and measurements were taken so that the longitudinal and width directions were aligned with the length of the sample. The average value of these measurements was taken as the breaking strength. 【0065】 (6) Percentage of thermal shrinkage after heating at 150°C for 30 minutes A polyester film was cut into strips 15 cm long and 1 cm wide. Lines parallel to the width direction were drawn 2.5 cm inward from each end of the length, and the distance L0 between the two parallel lines was measured. The strip samples were then heat-treated in a 150°C hot air oven for 30 minutes. After cooling, the distance L1 between the two parallel lines was measured. The thermal shrinkage rate (%) was calculated from the dimensions before and after treatment using the following formula. Thermal shrinkage rate (%) = (L0 - L1) / L0 × 100. 【0066】 [Manufacturing of polyester resin] The method for producing the polyester resin used in the polyester film in the examples is as follows. 【0067】 (PET raw material a) 86 parts by mass of terephthalic acid and 37 parts by mass of ethylene glycol were subjected to an esterification reaction at 255°C while distilling off water. After the esterification reaction was complete, 0.01 parts by mass of phosphoric acid, 0.02 parts by mass of magnesium acetate, 0.01 parts by mass of lithium acetate, and 0.01 parts by mass of antimony trioxide were added. Subsequently, under reduced pressure, the mixture was heated to 290°C and the temperature was increased to carry out a polycondensation reaction to obtain a virgin polyester resin that was substantially particle-free, had an intrinsic viscosity of 0.65 dl / g, and a rheometer viscosity ηH of 272 Pa·s. This was designated as PET raw material a. 【0068】 (PET raw material b) Virgin polyester raw material b-1 was obtained in the same manner as PET raw material a, except that the final torque of the stirrer used to determine the end of polymerization was changed. 【0069】 Furthermore, virgin polyester raw material b-2 was obtained in the same manner as virgin polyester raw material b-1, except that before adding the metal compound when producing virgin polyester raw material b-1, calcium carbonate with a volume-average particle size of 1.1 μm was added in an amount of 1.0 mass% relative to the polyester resin. Similarly, virgin polyester raw material b-3 was obtained in the same manner as virgin polyester raw material b-1, except that the particle species was alumina with a volume-average particle size of 0.03 μm added in an amount of 1.5 mass% relative to the polyester resin. Virgin polyester raw material b-1, virgin polyester raw material b-2, and virgin polyester raw material b-3 were blended in a mass ratio of 97.9:1.9:0.2 to obtain PET raw material b. 【0070】 (Recovered raw material A) A film was obtained by winding a film roll, which was molded by biaxial stretching using only PET raw material a according to a standard method. While winding the film roll, an aqueous solution was applied to one side of the film using a bar coater, with the solution being adjusted so that the solid content of the polyester resin was 5% by mass, containing 100 parts by mass of polyester resin (product name Z836, manufactured by Go-O Chemical Industry Co., Ltd.), 50 parts by mass of melamine-based crosslinking agent (product name MW12LF, manufactured by Sanwa Chemical Co., Ltd.), and 3 parts by mass of fluorine-based surfactant (product name RY2, manufactured by Go-O Chemical Industry Co., Ltd.). The solution was applied so that the coating thickness after drying was 0.1 μm. After drying and curing at 120°C for 1 minute, the film was wound up to obtain an optical film roll. Subsequently, the optical film roll was cut with a crusher with a screen diameter of Φ5 mm, and the cut used film was then added to a washing tank equipped with stirring blades. A 4.0% by mass sodium hydroxide aqueous solution was added to achieve a washing concentration of 10% by mass. Furthermore, 0.02% by mass of polyoxyethylene octylphenyl ether was added to the added sodium hydroxide aqueous solution. The washing tank was heated to 85°C, and the material was washed for 20 minutes while stirring at a stirrer speed of 200 rpm, after which it was rinsed with pure water. The polyester support, which had been vacuum-dried at 120°C, was then melt-kneaded in an extruder, and coarse particles and foreign matter were filtered out using a filter with a mesh size of 5 μm. The material was then extruded from the die in a strand form, and cut while cooling to form chips, which were used as the recovered raw material A. The obtained recovered raw material A had an intrinsic viscosity IV of 0.63 dl / g and a rheometer viscosity ηH of 197 Pa·s. 【0071】 (Recovered material B) A film was obtained by biaxial stretching using only PET raw material b as the raw material according to a standard method, and then winding the resulting film into a film roll. Next, this film was compressed and cut in a granulator to form cylindrical pellets of Φ5 mm × 20 mm, which were used as the recovered raw material B. The obtained recovered raw material B had an intrinsic viscosity IV of 0.60 dl / g and an ηH of 169 Pa·s. 【0072】 (Recovered material C) PET raw material a was melted in an extruder at 285°C, extruded in a sheet form from a die, and solidified in close contact with a rotating cooling drum at 25°C to obtain an unstretched film. This unstretched film was preheated to 70°C using a preheating roll, then heated to 90°C using a radiation heater from above and below, while being stretched 3.1 times in the longitudinal direction using the difference in peripheral speed between the rolls. Subsequently, it was cooled to 25°C using a cooling roll to obtain a uniaxially oriented (uniaxially stretched) film. Both sides of this film were subjected to corona discharge treatment in air to set the surface tension of the film to 55 mN / m. 【0073】 Next, the coating solution described later is applied to both sides of the uniaxially oriented film using a bar coater so that the coating thickness after drying and stretching is 100 nm per side. The uniaxially oriented film with the coating solution applied is then held with clips and led into an oven, where it is heated and dried with hot air at a temperature of 120°C and an airflow of 20 m / min. The film is then continuously led to the stretching process, where it is stretched 3.7 times in the width direction while being heated with hot air at a temperature of 100°C and an airflow of 15 m / min. The resulting biaxially oriented film is then continuously heat-treated with hot air at a temperature of 230°C and an airflow of 20 m / min for 15 seconds, after which it is relaxed by 5% in the width direction while being cooled from 230°C to 120°C, and then cooled to 50°C. After removing both ends in the width direction, the film is wound up to obtain a polyester film intermediate product with a thickness of 100 μm, and then the polyester film intermediate product is slit to a predetermined width. 【0074】 (coating liquid) The following aqueous solution was used, containing the following components in the following ratios when the solid content of the main component is 100 parts by mass, and having a concentration of 5.0% based on the solid content of the main resin. Main component (Polyester resin A as described in Japanese Patent Publication No. 2018-86605): 100 parts by mass Melamine-based crosslinking agent (Sanwa Chemical Co., Ltd. "Nicalac" (registered trademark) MW12LF): 50 parts by mass (based on solid content) Colloidal silica with an average particle size of 140 nm: 1.5 parts by mass Fluorine-based surfactant ("Pluscoat" (registered trademark) RY2, manufactured by Go-O Chemical Co., Ltd.): 1.5 parts by mass. 【0075】 The wound film described above is unwound and washed with water using a Roll-to-Roll device. In the washing tank, the coating is scraped off using a rotating metal brush. After scraping, the film is dewatered using a suction device, then passed through an oven heated to 120°C to evaporate the water, and then wound up to obtain a washed roll. The washed roll is unwound, cut with a crusher equipped with rotating blades, passed through a screen, and then stored in a flake storage silo. The flakes in the storage silo are blown into a storage hopper installed on a recovery device. The flakes are loaded in a fixed quantity onto a rotating disc with agitators inside a drum and rotated horizontally. The disc is rotated horizontally when the flake temperature reaches 200°C, as measured by a thermometer installed at the bottom of the drum. The extruder screw is started when the flake temperature reaches 200°C. The extruder is single-screw, and the screw L / D ratio is 35. The cylinder temperature is 260°C. Vacuum is drawn using a vent line attached to the cylinder, and the vacuum level is set to 1 kPa or less. The molten polymer is continuously removed of impurities using a three-layer screen mesh filter with mesh sizes of 300 μm, 20 μm, and 150 μm. Two pairs of these filters are provided, allowing for switching when one becomes clogged with impurities. The filtered polymer is discharged from a nozzle and cooled at a cooling rate of 120°C / sec while spraying cooling water to form gut. The gut is cut into chips using a cutting device with a rotating blade, then dewatered and blown into a storage silo to obtain the recovered raw material C. The obtained recovered raw material C had an intrinsic viscosity of 0.61 dl / g and an ηH of 140 Pa·s. 【0076】 <Example 1> 20% by mass of PET raw material a and 80% by mass of recovered raw material A were mixed and stirred in a blender, then dried under reduced pressure at 160°C for 8 hours, melted in an extruder at 285°C, melted and extruded into a sheet from a die, and solidified by being in close contact with a rotating cooling drum at 25°C to obtain an unstretched film. Using the difference in peripheral speed of heated rolls, the film was stretched 2.25 times in the longitudinal direction at 124°C (first stretch), then stretched 1.11 times in the longitudinal direction at 124°C (second stretch), and further stretched 2.10 times in the longitudinal direction at 117°C (third stretch), for a total of 5.25 times stretch. 【0077】 The film was held at both ends with clips, guided to a tenter, and stretched 4.10 times in the width direction at 110°C. Further stretching was performed by 1.0% in the TD direction while applying hot air at a heat-set (HS) temperature of 230°C for 3 seconds. Finally, it was relaxed by 2.63% in the width direction at 150°C to obtain an intermediate product with a thickness of 2.0 μm. This intermediate product was slit using a slitter to obtain a biaxially oriented polyester film roll with a product width of 500 mm. The evaluation results of the obtained film roll are shown in Table 1. 【0078】 <Examples 2-8, Comparative Examples 1-2> As shown in Tables 1 and 2, recycled polyester film was obtained in the same manner as in Example 1, except that the type of raw material, the amount of raw material used, the stretching ratio, the heat-fixing temperature, and the final thickness of the resulting film were changed. The properties obtained are shown in Table 2. 【0079】 [Table 1] 【0080】 [Table 2]

Claims

[Claim 1] A recycled polyester film comprising 40% by mass or more of recycled polyester raw material, wherein the film has a thickness of 1 μm or more and 10 μm or less, and the breaking strength in both the longitudinal and width directions is 230 MPa or more and 350 MPa or less. [Claim 2] The recycled polyester film according to claim 1, wherein the thermal shrinkage rate after heating at 150°C for 30 minutes in at least one of the longitudinal and width directions is 3.0% or less. [Claim 3] The recycled polyester film according to claim 1, wherein the intrinsic viscosity IV of the recycled polyester film is 0.55 dl / g or more and 0.65 dl / g or less. [Claim 4] A recycled polyester film according to any one of claims 1 to 3, wherein the Tmeta of the film observed by differential scanning calorimetry (DSC) is 195°C or higher and 235°C or lower.

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