Polyester film

Abstract

To provide a film which facilitates easy identification of a deterioration state during recycling.SOLUTION: There is provided a polyester film in which the gelation rate is 2.5 mass% or less relative to the entire polyester film and the odor detection intensity is 2.0 or more and 10 or less when analyzing a gas component after heating at 80°C for 60 minutes under sealing by the following analysis method using the following instrument. (Analytical instrument) "Flavo Tone" manufactured by Sanyo Chemical Industries, Ltd. (AnalySis Method) (1) 2.0 of a polyester film is finely cut and then is heated at 80°C for 60 minutes under sealing. (2) Gas after heating is encapsulated into a measurement container having a predetermined volume. (3) The gas in the measurement container is pressure-fed to an odor detection element by nitrogen gas for 60 seconds. (4) Odor intensity at a period every 0.1 second is detected and the highest detected intensity value in the total of 600 detections is defined as "an odor detection intensity".SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film. [Background technology]

[0002] In recent years, efforts to recycle polyester films have been accelerating as part of efforts to achieve the Sustainable Development Goals (SDGs). So-called horizontal recycling efforts are underway, in which used polyester films are recycled into raw materials and reused in polyester films for the same purpose. Regarding recycling, polyester films that reuse used release films, as shown in Patent Documents 1 and 2, and polyester films with release layers that can be easily peeled off to facilitate recycling have been studied. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-133373 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-17932 Summary of the Invention [Problem to be solved by the invention]

[0004] To achieve greater sustainability, it is necessary to achieve circular recycling, which involves endlessly regenerating raw materials from used film. However, the more polyester film is recycled, the faster it deteriorates and decomposes, primarily due to heat. For example, when used in the production of high-quality MLCCs (multilayer ceramic capacitors), LCD polarizers, or photoresist release films, there are concerns about yield degradation due to decomposition and degradation products during the MLCC, LCD polarizer, or photoresist manufacturing process. For films used in these applications, the incorporation of decomposition and degradation products into the film during recycling must be reduced to a level that does not affect yield. However, assessing the degradation state of film for recycling has traditionally required chemical analysis using organic solvents, making it difficult to easily identify the degradation state of film during recycling at sites such as logistics warehouses.

[0005] Therefore, an object of the present invention is to provide a film whose deterioration state can be easily identified during recycling. [Means for solving the problem]

[0006] A preferred embodiment of the present invention is as follows. 1. A polyester film having a gelation rate of 3.0% by mass or less based on the total mass of the polyester film, and which, after being heated in a sealed container at 80°C for 60 minutes, has an odor detection intensity of 2.0 or more and 10 or less when the gas components are analyzed using the following equipment and method: (analytical equipment) Sanyo Chemical Industries' "FlavoTone Tabletop Machine" (Analysis method) (1) 2.0 g of polyester film is cut into small pieces and then heated in a sealed container at 80°C for 60 minutes. (2) The heated gas is sealed in a measuring vessel of a specified volume. (3) The gas in the measurement container is pumped to the odor detection element using nitrogen gas for 60 seconds. (4) The odor intensity is detected every 0.1 seconds, and the highest detected intensity value among a total of 600 detections is defined as the “odor detection intensity.” 2. The number of protrusions obtained using the following method is 0.030 / cm 2 1. The polyester film according to 1., (Method for measuring the number of protrusions) The number of protrusions is estimated by placing two 10cm square films on top of each other with the surfaces to be measured, applying an applied voltage and bringing them into contact with each other using electrostatic force, and estimating the height from the interference fringes generated by the coarse protrusions on the film surface. The interference fringes are 0.27μm for a single ring, 0.54μm for a double ring, and 0.81μm or more for a triple ring, and the number of interference fringes with double rings or more is counted as the number of protrusions. The number of protrusions is counted 50 times, and the total number of coarse protrusions counted over 50 times is used to calculate the total area of ​​5000cm. 2 Divide by this to find the number of protrusions per unit area. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a film whose deterioration state can be easily identified during recycling. [Brief explanation of the drawings]

[0008] [Figure 1] This is a conceptual diagram of horizontal recycling. [Figure 2] FIG. 2 is a conceptual diagram showing peeling of an inorganic material from a laminate having a polyester film and an inorganic material, according to an example of a method for producing a recycled polyester film. [Figure 3] FIG. 1 is a conceptual diagram showing a manufacturing process of a recycled polyester film according to an example of a manufacturing method of a recycled polyester film. DETAILED DESCRIPTION OF THE INVENTION

[0009] In light of the above, the inventors conducted extensive research and discovered that the above problem can be solved by incorporating an identification factor into the manufacturing process, making it possible to indirectly quantify the amount of heat received by the film.

[0010] The present invention will be described in further detail below.

[0011] The polyester of the polyester film used in the present invention refers to a polyester resin composition obtained by polycondensation of a dicarboxylic acid component and a diol component.

[0012] Examples of the dicarboxylic acid component in the present invention include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, malonic acid, dimer acid, etc. More preferred embodiments of the dicarboxylic acid in the present invention are terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, or alkyl esters thereof, since they have a high melting point and can give polyester compositions that are easily processed into films, fibers, etc.

[0013] The diol component in the present invention may be an aliphatic diol such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,2-hexanediol, 1,6-hexanediol, or neopentyl glycol; a saturated alicyclic primary diol such as cyclohexanedimethanol, cyclohexanediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecanediethanol, decalindimethanol, or decalindiethanol; a saturated heterocyclic primary diol containing a cyclic ether such as isosorbide; or Examples of suitable diols include alicyclic diols such as cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, and adamantanediol, and aromatic diols such as paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, and 9,9'-bis(4-hydroxyphenyl)fluorene. In addition to diols, polyfunctional alcohols such as trimethylolpropane and pentaerythritol can also be used as long as they do not impair the effects of the present invention. Among these, diols with a boiling point of 230°C or less are preferred because they can be easily distilled out of the reaction system, and aliphatic diols are more preferred because they are low cost and highly reactive. Furthermore, ethylene glycol is particularly preferred from the viewpoint of the mechanical properties of the resulting polyester resin composition and molded articles thereof.

[0014] The polyester resin composition of the present invention is not particularly limited, but preferably contains, as a main constituent, at least one structural unit selected from ethylene terephthalate, ethylene-2,6-naphthalate, propylene terephthalate, butylene terephthalate, hexamethylene terephthalate, cyclohexanedimethylene terephthalate, propylene-2,6-naphthalate, butylene-2,6-naphthalate, hexamethylene-2,6-naphthalate, and cyclohexanedimethylene-2,6-naphthalate units. Among these, polyesters containing ethylene terephthalate as a main constituent unit are particularly preferred due to their excellent moldability. Two or more polyesters may be mixed, or copolymerized polyesters may be used.

[0015] The polyester film of the present invention preferably has a gelation rate of 3.0% by mass or less relative to the total polyester film. It is known that the gelation rate of polyester films increases with the amount of heat they receive. The presence of gelled material within the film affects the unevenness of the film surface, causing various problems, including missing coatings when coating the film surface. A lower amount of gelled material or gelation rate is preferable because it reduces problems during coating processing on the film surface. Meanwhile, in the horizontal recycling process described below, a heat-exposed process is involved, and the gelation rate increases with repeated recycling. Therefore, a lower gelation rate of polyester film increases the number of times it can be recycled. Furthermore, if a predetermined gelation rate can be detected by simple measurement and recycling of the film can be discontinued, it is possible to reduce the cost of the recycling process and improve the quality of the recycled film.

[0016] The polyester film of the present invention preferably has an odor detection intensity of 2.0 or more and 10 or less when heated in a sealed state at 80° C. for 60 minutes and then analyzed for gas components using the following equipment and method. (analytical equipment) Sanyo Chemical Industries' "FlavoTone Tabletop Machine" (Analysis method) (1) 2.0 g of polyester film is cut into small pieces and then heated in a sealed container at 80°C for 60 minutes. (2) The heated gas is sealed in a measuring vessel of a specified volume. (3) The gas in the measurement container is pumped to the odor detection element using nitrogen gas for 60 seconds. (4) The odor intensity is detected every 0.1 seconds, and the highest detected intensity value among a total of 600 detections is defined as the “odor detection intensity.”

[0017] This embodiment allows for a correlation between the decrease in odor detection intensity due to heating of the polyester film and the increase in gelation rate of the entire polyester film. This makes it possible to easily determine the timing for transitioning from so-called horizontal recycling, in which used polyester film is recycled into raw materials (recycled) and reused in polyester film for the same purpose, to thermal recycling, in which the film is burned as a thermal energy source, or chemical recycling, in which the film is decomposed into raw materials through chemical treatment. If the odor detection intensity is below 2.0, repeated recycling may result in a complete decrease in odor detection intensity, making it difficult to correlate with the increase in gelation rate that accompanies repeated recycling. If the odor detection intensity exceeds 10, the odor of the film itself may cause quality abnormalities in processes using the film. From the same perspective, the odor detection intensity is more preferably 4.0 or more and 8.0 or less.

[0018] The number of protrusions in the polyester film of the present invention is 0.030 / cm 2 It is preferable that the number of particles is 0.025 particles / cm or less, and more preferably 0.025 particles / cm 2The following is a summary. It is known that in polyester films, the catalyst residues used during the polymerization of polyester resins aggregate due to the amount of heat received. Although these are removed by a filter, some of the aggregates that pass through remain inside the film, forming coarse protrusions and causing various problems, such as missing coatings when coating the film surface. A low number of coarse protrusions is preferable because it reduces problems during coating processing on the film surface. On the other hand, in the horizontal recycling process described below, there is a process in which heat is applied, and it is expected that the number of protrusion-forming materials will increase with repeated recycling. Therefore, a low number of protrusions on a polyester film increases the number of times it can be recycled. Furthermore, if a certain number of protrusions can be detected by simple measurement and the recycling of the film can be discontinued, it is possible to reduce the cost of the recycling process and improve the quality of the recycled film. The number of protrusions is determined using the method described in the examples.

[0019] The number of protrusions is 0.030 / cm 2 Because the following correlation can be established between the decrease in odor detection intensity due to heating of the polyester film and the increase in the number of protrusions, it becomes possible to easily identify the timing to transition from so-called horizontal recycling, in which used polyester film is recycled into raw materials and reused in polyester film for the same purpose, to thermal recycling, in which it is burned as a thermal energy source, or chemical recycling, in which it is decomposed into crude raw materials through chemical processing.

[0020] In this invention, horizontal recycling refers to collecting used products to be recycled and returning them to their original state. For example, referring to a release polyester film for molding dielectric materials for multilayer ceramic capacitors, referring to Figures 1 and 2, polyester film A1 is manufactured at a polyester film manufacturing facility and appropriately processed in a converter to obtain release polyester film 2. Alternatively, polyester film is manufactured at a polyester film manufacturing facility to obtain release polyester film 2. The user then deposits the dielectric material of the multilayer ceramic capacitor on release polyester film 2 as inorganic layer 7, and then peels inorganic layer 7 from release polyester film 2. The peeled release polyester film 3 corresponds to the used product, and release polyester film 3 or a portion thereof is appropriately processed as recycled raw material 4 and used to manufacture a new recycled polyester film. Horizontal recycling is achieved by appropriately processing the resulting recycled polyester film to produce a release polyester film containing recycled raw material that exhibits physical properties suitable for molding dielectric materials for multilayer ceramic capacitors. In the above example, a new recycled polyester film is produced, but if a film that will not be used as a dielectric material for a multilayer ceramic capacitor is produced, it is not horizontal recycling but simple recycling.

[0021] The method for extracting the recycled raw material 4 and recycled polyester film will be described with reference to Figures 2 and 3, taking a release polyester film for molding the dielectric material of the multilayer ceramic capacitor as an example. A peeling process is performed on a laminate 5 consisting of the dielectric material (inorganic layer 7) of the multilayer ceramic capacitor molded on a release polyester film 2 to obtain a peeled release polyester film 3 and the dielectric material (inorganic layer 7) of the multilayer ceramic capacitor. The peeled release polyester film 3 contains a polyester film A1 (conveniently named polyester film A to distinguish it from the recycled polyester film described below), and the dielectric material (inorganic layer 7) of the multilayer ceramic capacitor contains an inorganic substance. The coating layer 6 is washed from the peeled release polyester film 3 as needed, and then cut, remelted, and pelletized as needed to obtain a portion 9 of the polyester film A. This portion 9 of the polyester film A is the same as the recycled raw material 4. If necessary, new polyester resin raw material 10 is added and the mixture is molded into a film by melt extrusion or the like to obtain a recycled polyester film.

[0022] In the film of this embodiment, odor substances sublimate with the amount of heat received, resulting in a decrease in odor detection intensity. Therefore, by measuring the odor detection intensity of the film, it is possible to quantify the film's quality (gelation rate) as odor detection intensity. While measuring the gelation rate typically requires complicated procedures, as described in the Examples section, this embodiment allows odor detection intensity to be measured in a short time using only a simple heater such as an oven and analytical equipment, making it possible to indirectly measure the gelation rate. In particular, in horizontal recycling processes, it is necessary to determine whether the recycled polyester film processed by the user can be reused for horizontal recycling. This embodiment simplifies the quality and assessment of the recycled polyester film.

[0023] The odor detection intensity can be set to 2.0 or more and 10 or less by incorporating an odorant into the polyester film. Examples of odorants include hexane, ethyl acetate, ethyl butyrate, butyl butyrate, methanol, diethyl carbonate, toluene, d-limonene, bornan-2-one, cis-3-hexenol, β-phenylethyl alcohol, citral, L-carvone, γ-undecalactone, eugenol, linalyl acetate, menthol, benzaldehyde, benzoic acid, vanillin, hexanal, ethanol, pentyl valerate, linalool, and 2-propanol, but the odorant to be incorporated into the polyester film of the present invention is not particularly limited.

[0024] The method of incorporating an odorant into the polyester film of the present invention is not particularly limited. One or more odorants can be incorporated into the polyester film by known methods, such as adding them during the polycondensation reaction of the polyester resin composition, or kneading them with the polyester resin composition after the polycondensation reaction using a twin-screw kneading extruder.

[0025] In the polyester film manufacturing process, the film-forming process can be performed by any known film-forming process, such as T-die extrusion or stretching. A single-screw or twin-screw extruder can be used. Specifically, the film is preferably formed by the following method.

[0026] The polymer melted and extruded in the extruder is preferably filtered through a filter. Since foreign matter entering the film can cause large protrusion defects, it is effective to use a filter with high-precision collection efficiency, capturing, for example, 95% or more of foreign matter 5 μm or larger. The film is then extruded into a sheet through a slit die and cooled and solidified on a casting roll to obtain an unstretched film. The unstretched film that lands on the casting roll can be adhered to the cast using electrostatic force using a pinning device. After the film is cooled and adhered to the casting roll, it can be peeled off from the casting roll using a peeling roll and introduced into the next stretching process. When stretching, the film is stretched in the longitudinal and width directions using known methods. The stretched film is cooled in a conveying process, then the edges are cut and wound up to obtain an intermediate product. The intermediate product can then be slit to the appropriate width and length in a slitting process and wound onto a core. [Example]

[0027] The methods for measuring and evaluating the property values ​​in the examples and comparative examples are as follows.

[0028] (1) Content of odorous substances in polyester film (unit: mass ppm) The polyester film was cut into small pieces and heated at 290°C for 30 minutes in a nitrogen atmosphere. The generated gas was collected in an adsorption tube. The gas was then analyzed using a PerkinElmer TurboMatrix 650 gas chromatograph and a Shimadzu GC / MS-QP2010Plus. The detected components were quantified using a calibration curve prepared using standard substances.

[0029] (2) Odor detection strength by odor sensor 2.0 g of polyester film was cut into small pieces and heated at 80°C for 60 minutes in a sealed container. The heated gas was then sealed in a measurement container of a specified volume. The gas in the measurement container was pressure-fed with nitrogen gas at 0.06 L / min to an odor detection element (element model number: FlavoTone SS01) for 60 seconds. The measurement gas was pressure-fed to the odor detection element, and the odor intensity was detected every 0.1 seconds. The highest detected intensity value out of a total of 600 detections was recorded as the "odor detection intensity."

[0030] (3) Gel rate The polyester film was pulverized using a freeze pulverizer (manufactured by Sprex CertiPerp) and weighed into a stainless steel beaker at 0.5 g. After vacuum drying at 50°C for 2 hours using a vacuum dryer, the film was heat-treated at 300°C for 6 hours under a 1% oxygen / nitrogen flow (flow rate: 0.5 L / min). The film was dissolved in 20 ml of o-chlorophenol at 160°C for 1 hour and allowed to cool. The solution was filtered using a glass filter (3G-3), and the glass filter was washed with dichloromethane. The glass filter was dried at 130°C for 2 hours, and the masses before and after filtration were compared. The gelation rate was calculated from the mass of the filtered material (gelled product).

[0031] (4) Number of polarization defects The film roll obtained by the method described below was transported at a line speed of 10 m / min under a tension of 250 N / m. The film was visually inspected across 1 m of width through a polarizing plate under fluorescent lighting, and the number of polarization defects that appeared over the 100 m of transport was counted. Observing the film with polarized light made it possible to detect gel defects present inside the film. The number of polarization defects counted was used to evaluate the film according to the following criteria. ○: 20 polarized defects / 100m 2 less than. ×: 20 polarization defects / 100m 2 That's all.

[0032] (5) Number of protrusions The number of protrusions was estimated by placing two 10cm square films on top of each other with the surfaces to be measured, applying an applied voltage and bringing them into contact with each other using electrostatic force, and estimating the height from the interference fringes generated by the coarse protrusions on the film surface. The interference fringes were 0.27μm for a single ring, 0.54μm for a double ring, and 0.81μm or more for a triple ring, and the number of interference fringes with double rings or more was counted as the number of protrusions. The number of protrusions was counted 50 times, and the total number of coarse protrusions counted over 50 times was used to calculate the total area of ​​5000cm. 2 The number of protrusions per unit area was calculated by dividing the area by .

[0033] (6) Creation of recycled materials A polyester film obtained by the method described below is provided with a release layer in the process described below to produce a green sheet, and the film is wound up after use to produce recycled raw materials.

[0034] First, the wound film is unwound and washed with water using a roll-to-roll device. In the water washing tank, a rotating metal brush is used to scrape off any green sheet residue and release layer. After scraping, the film is vacuumed to remove the water, then passed through an oven heated to 120°C to evaporate the water, and then wound up to obtain a cleaned roll.

[0035] After washing, the roll is unwound, cut into pieces using a crusher with rotary blades, passed through a screen, and then stored in a flake storage silo.

[0036] The flakes in the storage silo are blown into a storage hopper installed on the recovery device. A fixed amount of flakes are placed in the drum onto a rotating disc equipped with agitating blades, which is rotated horizontally. The disc is used to measure the temperature of the flakes, as measured by a thermometer installed below the drum. The extruder screw is started when the temperature of the flakes reaches 200°C. The extruder is single-screw, with a screw L / D of 35. The cylinder temperature is 260°C. A vacuum is drawn through a vent line attached to the cylinder, with the vacuum level kept below 1 kPa. The molten polymer is continuously filtered using a stack of three screen mesh filters with openings of 300 μm, 20 μm, and 150 μm. Two pairs of filters are provided, allowing for switching if clogging occurs. The filtered polymer is discharged from the nozzle and cooled at a cooling rate of 120°C / sec while spraying cooling water to form a gut. The gut is cut into chips using a cutting device with a rotary blade, and after dehydration, the chips are sent to a storage silo. The resulting chips are used as recycled raw materials.

[0037] The mass ratio of recycled raw materials to the polyester pellets fed to the extruder for the polyester B layer was 100%, and the polyester was recycled multiple times. The number of times recycling was performed was the number of times the following steps (A) to (H) were repeated. (A) A process for cleaning the surface of a polyester film. (B) A step of preparing flakes from the washed polyester film. (C) A step of drying the flakes obtained above. (D) A step of melting the dried flakes in an extruder to extrude a polyester. (E) A step of filtering the extruded polymer through a polymer filter. (F) A step of discharging the polyester filtered through the polymer filter from a nozzle. (G) The polyester discharged from the die is cooled, then cut into recycled raw materials. (H) A step of producing a recycled polyester film so that the recycled raw material is contained in 100% by mass of the layer B.

[0038] (The process involves adding a release layer to polyester film to create a green sheet, which is then wound up after use.) (Release layer application) A crosslinking primer layer (manufactured by Dow Corning Toray Silicones Co., Ltd. under the trade name BY24-846) was applied to a polyester film roll using a gravure coater to a 1% solids content, then dried to a thickness of 0.1 μm. The resulting coating was then dried and cured at 100°C for 20 seconds. Within one hour, a coating solution containing 100 parts by weight of an addition-reaction type silicone resin (manufactured by Dow Corning Toray Silicones Co., Ltd. under the trade name "LTC"® 750A) and 2 parts by weight of a platinum catalyst (manufactured by Dow Corning Toray Silicones Co., Ltd. under the trade name SRX212) was applied to a 5% solids content using a gravure coater to a thickness of 0.1 μm. The resulting coating was then dried and cured at 120°C for 30 seconds, after which the film was taken up to obtain a release film.

[0039] (Green sheet molding) Glass beads with a number average particle size of 2 mm were added to 100 parts by mass of barium titanate (manufactured by Fuji Titanium Kogyo Co., Ltd., product name HPBT-1), 10 parts by mass of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., product name BL-1), 5 parts by mass of dibutyl phthalate, and 60 parts by mass of toluene-ethanol (30:30 mass ratio), and the mixture was mixed and dispersed using a jet mill for 20 hours, followed by filtration to prepare a paste-like ceramic slurry. The resulting ceramic slurry was applied to a release film using a die coater to a dry thickness of 2 μm, dried, and wound up to obtain a green sheet.

[0040] [Example 1] (1) Preparation of polyester raw materials for polyester film (Collection of polyester resin composition) A slurry consisting of 86 parts by mass of terephthalic acid and 37 parts by mass of ethylene glycol (1.15 times the molar ratio of terephthalic acid) was gradually added to an esterification reactor containing 105 parts by mass of BHT (bishydroxyethyl terephthalate) dissolved at 250°C, and the esterification reaction was allowed to proceed while distilling off water. The temperature in the reaction system was controlled to 245-250°C, and the esterification reaction was terminated when the reaction rate reached 95%, and 105 parts by mass of the resulting esterification product (equivalent to 100 parts by mass of PET (polyethylene terephthalate)) was charged in a molten state into a polymerization reactor equipped with a distillation device.

[0041] As an odorant, ethyl butyrate was added as an ethylene glycol solution to a concentration of 30 ppm by mass. Subsequently, the pressure in the polymerization reaction vessel was gradually reduced to 0.13 kPa or less in 35 minutes, and at the same time, the temperature was gradually increased to 279°C, and the polymerization reaction was carried out until the intrinsic viscosity of the polyester resin composition reached 0.625. Thereafter, the polycondensation reaction vessel was returned to normal pressure with nitrogen gas, and the mixture was discharged into cold water in the form of a strand from a nozzle and pelletized into a cylindrical shape using an extrusion cutter to obtain a polyester resin composition.

[0042] Separately, an aqueous slurry of divinylbenzene / styrene copolymer crosslinked particles having a volume average particle size of 1.0 μm and a volume shape factor f=0.51, obtained by a monomer adsorption method, was added to the above polyester resin composition pellets using a vented twin-screw kneader to obtain master pellets containing 1 part by mass of divinylbenzene / styrene copolymer crosslinked particles having a volume average particle size of 1.0 μm per 99 parts by mass of the polyester resin composition.

[0043] The volume shape factor f is expressed by the following equation: f=V / Dm 3 where V is the particle volume (μm 3 ), Dm is the maximum diameter (μm) of the particle on its projected surface. The volume shape factor f is at its maximum of π / 6 when the particle is spherical.

[0044] (Manufacture of polyester film rolls) These polyesters were each dried under reduced pressure at 160°C for 8 hours to a moisture content of 100 ppm by mass, then fed into separate extruders, melt-extruded at 275°C, filtered through a high-precision filter with a collection efficiency of 95% for particles of 5 μm or more, and then joined and laminated in a rectangular three-layer joining block to form a three-layer laminate consisting of polyester layer A / polyester layer B / polyester layer A. The master pellets described above were used for polyester layer A, and the polyester resin composition described above was used for polyester layer B.

[0045] The film was then cast using an electrostatic casting method through a slit die maintained at 285°C, followed by cooling and solidification 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 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 width direction at 110°C in a tenter. The film was then cooled to 35°C at a width shrinkage rate of 18% / min. This cooling process employed a roll system, with the roll temperature set to 30°C and the cooling time set to 15 seconds. The film was then heat-treated at 195°C, resulting in a three-layer polyester film with a total thickness of 31 μm, a laminate thickness of polyester layer A / polyester layer B / polyester layer A = 1.0 μm / 29 μm / 1.0 μm, and a width of 5.1 m. This was then wound into an intermediate product roll. Samples were taken from the resulting intermediate product roll and evaluated. The results are shown in Table 1. In Example 1, the odor sensor value decreased with the number of recycling attempts, while the gelation rate and the number of polarization defects increased, resulting in a correlation between the odor detection intensity and the gelation rate.

[0046] [Example 2] A polyester resin composition and a polyester film were obtained in the same manner as in Example 1, except that the odorant was changed from ethyl butyrate to limonene. The results showed a correlation between odor detection intensity and gelation rate, etc.

[0047] [Comparative Example 1] Except for changing the amount of ethyl butyrate added from 30 ppm by mass to 1000 ppm by mass, a polyester resin composition and a polyester film were obtained in the same manner as in Example 1. Because the amount of odorous substance added was too large, the odor detection intensity did not decrease even after repeated recycling, and no correlation could be found between the odor detection intensity and the gelation rate, etc.

[0048] Comparative Example 2 Except for changing the amount of ethyl butyrate added from 30 ppm by mass to 0 ppm by mass, a polyester resin composition and a polyester film were obtained in the same manner as in Example 1. Because no odorant was added, the odor detection intensity did not decrease even after repeated recycling, and no correlation could be found between the odor detection intensity and the gelation rate, etc.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3] [Industrial Applicability]

[0052] The polyester film of the present invention is particularly suitable for use as a polyester film release agent suitable for horizontal recycling. [Explanation of symbols]

[0053] 1 Polyester film A 2. Polyester release film 3 Peeled release polyester film 4. Recycled materials 5. Laminate 6 coating layers 7 Inorganic layer 8 Inorganic substances and parts thereof contained in the inorganic layer 9 Part of polyester film A 10 New polyester resin raw materials 11 Recycled polyester film

Claims

1. A polyester film having a gelation rate of 2.5% by mass or less based on the total mass of the polyester film, and having an odor detection intensity of 2.0 or more and 10 or less when heated in a sealed state at 80°C for 60 minutes and then analyzed for gas components using the following equipment and method: (analytical equipment) Sanyo Chemical Industries "FlavoTone Desktop Machine" (Analysis method) (1) 2.0 g of polyester film was cut into small pieces and then heated in a sealed container at 80° C. for 60 minutes. (2) The heated gas is sealed in a measurement vessel of a predetermined volume. (3) The gas in the measurement container is pumped into the odor detection element with nitrogen gas for 60 seconds. (4) The odor intensity is detected every 0.1 seconds, and the highest detected intensity value among a total of 600 detections is defined as the "odor detection intensity."

2. The number of protrusions obtained by the following method is 0.030 / cm ２ The polyester film according to claim 1, wherein (Method for measuring the number of protrusions) The number of protrusions is estimated by placing two 10 cm square films with their measurement surfaces facing each other, applying a voltage to make them adhere together by electrostatic force, and estimating the height from the interference fringes generated by the large protrusions on the film surface. The interference fringes are 0.27 μm for a single ring, 0.54 μm for a double ring, and 0.81 μm or more for a triple ring, and the number of interference fringes with double rings or more is counted as the number of protrusions. The counting is repeated 50 times, and the total number of coarse protrusions counted over the 50 times is calculated for a total area of ​​5000 cm. ２ Divide by this to find the number of protrusions per unit area.

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