Polyester film

Abstract

To provide a polyester film excellent in uniformity of elongation at a glass transition temperature or higher.SOLUTION: When pyrolysis gas chromatography-mass spectrometry (pyrolysis GC / MS) is performed, any one or more of Structural Formulae 1 to 3 are detected, and a peak area value per unit mass detected as Structural Formulae 1 to 3 is 150 to 2000a. u. / μ g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film that exhibits excellent uniformity of elongation at temperatures equal to or higher than its glass transition temperature and exhibits excellent luminescence properties in response to excitation light of a specific wavelength. [Background technology]

[0002] Polyesters are used in a variety of industrial fields due to their ease of processing, and film products made from these polyesters play an important role in modern life, including industrial applications, optical products, packaging, and magnetic recording tape.

[0003] Patent Document 1 discloses a polyester film made from recycled resources that contains a fluorescent whitening agent that is excited by ultraviolet light and emits blue visible light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-104955 Summary of the Invention [Problem to be solved by the invention]

[0005] Recent advances in smart devices, electric vehicles, and IoT have led to a rapid increase in the number of electronic devices, such as CPUs, installed in these devices. This has led to a corresponding increase in the quality of multilayer ceramic capacitors (MLCCs), which are crucial for driving these devices. The typical manufacturing method for MLCCs involves coating and laminating ceramic green sheets and electrodes onto a polyester film substrate with a release layer. The substrate is then dried and solidified, and the resulting laminate is then peeled from the release film, followed by lamination of multiple layers and firing. As the quality of MLCCs continues to improve, it is becoming increasingly important to accurately determine the coating positions of the ceramic green sheets and electrodes during the coating, lamination, and drying process. This has created a strong demand for polyester films with excellent elongation uniformity above their glass transition temperatures. Polyester films with excellent elongation uniformity above their glass transition temperatures are also in demand for applications other than MLCCs.

[0006] However, the polyester film disclosed in Patent Document 1 has a multilayer structure with three layers, A / B / A, and further contains a fluorescent brightening agent in layer B, which can cause uneven dispersion of the fluorescent brightening agent and insufficient uniformity in elongation above the glass transition temperature.

[0007] Therefore, an object of the present invention is to provide a polyester film having excellent uniformity of elongation at temperatures above the glass transition temperature. [Means for solving the problem]

[0008] In order to solve the above problems, a preferred embodiment of the polyester film of the present invention has the following structure. (1) When pyrolysis gas chromatography mass spectrometry (pyrolysis GC / MS) was performed using the following measurement device and under the following measurement conditions, one or more of the following structural formulas 1 to 3 was detected: A polyester film having a peak area per unit mass detected as structural formulas 1 to 3 of 150 to 2000 a.u. / μg.

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[0012] (Measuring equipment) Pyrolysis furnace:PY-3030iD GC:7890A MS: JMS‐Q1050GC (Measurement conditions) Pyrolysis temperature: 600℃ Column: Ultra ALLOY-5 (MS / HT) Heating conditions: Hold at 40°C for 3 minutes, then heat to 320°C at 20°C / min, and hold at 320°C for 18 minutes Inlet: 300℃ Mode: Split (20:1) 1.5mL / min constant flow Ionization method: EI+ Scan range: m / z 10,000-800,000 Scan speed: 0.5s / scan (2) 550 nm emission peak intensity with 350 nm excitation light (I 550nm ) and 370 nm emission peak intensity (I 370nm ) satisfies the following formula (i): (i) 5≦(I 550nm ) / (I 370nm )×100≦20 (3) The polyester film according to (1) or (2), wherein the content of alkali metal elements contained in the polyester film is 1.5 ppm by mass or more and 40.0 ppm by mass or less. (4) The polyester film according to any one of (1) to (3), wherein the alkali metal element contained in the polyester film is sodium. (5) The polyester film according to any one of (1) to (4), which is used for release purposes. [Effects of the Invention]

[0013] According to the present invention, a polyester film having excellent uniformity of elongation at temperatures equal to or higher than the glass transition temperature can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0014] A preferred embodiment of the present invention will be described in detail below with reference to a specific example.

[0015] When the polyester film of the present invention is subjected to pyrolysis gas chromatography mass spectrometry (pyrolysis GC / MS) using the following measuring device and under the following measuring conditions, it is preferable that one or more of the following structural formulas 1 to 3 are detected, and the peak area per unit mass detected as structural formulas 1 to 3 satisfies 150 to 2000 a.u. / μg.

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[0017] [ka]

[0018] [ka]

[0019] (Measuring equipment) Pyrolysis furnace:PY-3030iD GC:7890A MS: JMS‐Q1050GC (Measurement conditions) Pyrolysis temperature: 600℃ Column: Ultra ALLOY-5 (MS / HT) Heating conditions: Hold at 40°C for 3 minutes, then heat to 320°C at 20°C / min, and hold at 320°C for 18 minutes Mode: Split (20:1) 1.5mL / min constant flow Ionization method: EI+ Scan range: m / z 10,000-800,000 Scan speed: 0.5s / scan The Ultra ALLOY-5 (MS / HT) column is a GC capillary column manufactured by Frontier Labs, Inc., and its stationary phase is 5% diphenyldimethylpolysiloxane.

[0020] Structural Formulas 1 to 3 are components having a conjugated system, and the inclusion of components having structural formulas 1 to 3 may result in polyester films that exhibit excellent uniformity in elongation above the glass transition temperature, leading to improved precision in subsequent processes. This is believed to be because structural formulas 1 to 3 are components having a conjugated system, improving stretchability regardless of the orientation of the polyester. Furthermore, it is believed that the presence of components having structural formulas 1 to 3 interspersed among the polyester molecular chains alleviates restrictions on molecular chain motion.

[0021] From the viewpoint of controlling the uniformity of elongation, the peak area value per unit mass (au / μg) detected as Structural Formulas 1 to 3 is preferably 150 or more, more preferably 500 or more, and even more preferably 1000 or more. If the peak area value per unit mass (au / μg) detected as Structural Formulas 1 to 3 exceeds 2000, the conjugated components will be scattered, causing unevenness, reducing the Young's modulus of the polyester film and making it more susceptible to breakage, which may result in poor uniformity of elongation. The detailed method for determining the peak area value will be described later.

[0022] Examples of means for achieving a peak area value per unit mass (au / μg) of 150 to 2000 detected as structural formulas 1 to 3 include a method of adding a monomer consisting of structural formulas 1 to 3 and its isotopes, or an oligomer or polymer having structural formulas 1 to 3 and its isotopes at the repeating unit or terminal thereof. The method of addition is not particularly limited, but addition prior to the step of producing an unstretched sheet is preferred from the viewpoint of efficiently dispersing the components consisting of structural formulas 1 to 3.

[0023] The polyester film of the present invention has a 550 nm emission peak intensity (I 550nm ) and 370 nm emission peak intensity (I 370nm ) preferably satisfies the following formula (i): (i) 5≦(I 550nm ) / (I 370nm )×100≦20 (I 550nm ) / (I 370nm ) × 100 is 5 or more and 20 or less, when a black light is irradiated onto the polyester film, the components consisting of structural formulas 1 to 3 have good luminescence in the visible light region, and the film may be suitably used for appearance inspection purposes. In particular, when a layer such as a release layer or a release target layer is provided, it becomes difficult to detect transmitted light, so that excellent luminescence in the visible light region may be more suitably used. From the viewpoint of preventing missed detection in inspection purposes, (I 550nm ) / (I 370nm ) × 100 is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more. 550nm ) / (I 370nm ) × 100 exceeds 20, the emission peak intensity is high and the emission position may become unclear, which is undesirable. The method for measuring the emission peak intensity will be described later. Examples of means for satisfying formula (i) include a method of adding a monomer consisting of the above structural formulas 1 to 3 and their isotopes, or an oligomer or polymer having the structural formulas 1 to 3 and their isotopes in a repeating unit or at a terminal.

[0024] The amount of alkali metal element contained in the polyester film of the present invention is preferably 1.5 ppm by mass or more and 40.0 ppm by mass or less. When the amount of alkali metal element is within the preferred range, the hydrophilic and hydrophobic portions of the polyester film are uniformly dispersed, thereby increasing the affinity between the components represented by Structural Formulas 1-3 and the hydrophobic portions, which may prevent scattering due to heat or facilitate control of the dispersibility of the components represented by Structural Formulas 1-3, resulting in excellent applicability of the release agent. If the amount of alkali metal element contained in the polyester film is less than 1.5 ppm by mass, the dispersibility of the components represented by Structural Formulas 1-3 may become uneven, which is undesirable. If the amount of alkali metal element contained in the polyester film exceeds 40.0 ppm by mass, components having a conjugated system may be scattered. When used as a process release film, defects may occur during application to the release target, which is undesirable from the standpoint of quality stability. The amount of alkali metal element contained in the polyester film is more preferably 3.0 ppm by mass or more and 30.0 ppm by mass or less, and even more preferably 6.0 ppm by mass or more and 20.0 ppm by mass or less.

[0025] Preferred examples of the alkali metal element contained in the polyester film of the present invention include lithium, sodium, potassium, rubidium, cesium, and francium, with sodium being more preferred from the viewpoint of versatility and ease of handling.

[0026] The method for incorporating an alkali metal element into the polyester film of the present invention is not particularly limited, and may be a method of adding an alkali metal compound during the polymerization process or film formation process of the polyester film, or a method of contacting the polyester film with an aqueous solution containing an alkali metal element.

[0027] The polyester film of the present invention refers to a film containing polyester as the main component, where the main component is a component that accounts for more than 50% by mass of the total components of the film (100% by mass).

[0028] The polyester referred to in the present invention is a polyester comprising a dicarboxylic acid component and a diol component. In this specification, the term "component" refers to the smallest unit obtainable by hydrolysis of a polyester. Examples of dicarboxylic acid components constituting such polyesters include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid. Furthermore, the polyester film of the present invention preferably contains terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid in total at 95 mol% or more, and more preferably 99 mol% or more, of 100 mol% of the acid components of the polyester.

[0029] Examples of diol constituent components constituting such polyesters include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol; alicyclic diols such as cyclohexanedimethanol and spiroglycol; and diols in which two or more of the above-mentioned diols are linked together.

[0030] From the viewpoints of mechanical properties and transparency, the polyesters used in the present invention are preferably polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalenedicarboxylate (PEN), PET obtained by copolymerizing a portion of the dicarboxylic acid component with isophthalic acid or naphthalenedicarboxylic acid, or PET obtained by copolymerizing a portion of the diol component with cyclohexanedimethanol, spiroglycol, or diethylene glycol. Of these, polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are particularly preferred. That is, the polyester film of the present invention preferably has an aromatic ring, and is preferably a film of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or polyethylene-2,6-naphthalenedicarboxylate (PEN), with polyethylene terephthalate being more preferred. Furthermore, these PET, PBT, and PEN may contain copolymer components.

[0031] The polyester can be produced by a known method, and it is preferable to use a polyester having an intrinsic viscosity in the range of 0.50 to 0.80 dL / g, more preferably 0.50 to 0.75 dL / g, and even more preferably 0.50 to 0.70 dL / g. The intrinsic viscosity is measured using a value calculated from the solution viscosity measured in orthochlorophenol at 25°C using the following formula: ηsp / C=[η]+K[η] 2 C Here, ηsp = (solution viscosity / solvent viscosity)-1, C is the mass of dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (0.343). The solution viscosity and solvent viscosity are measured using an Ostwald viscometer. The unit is [dL / g].

[0032] The polyester film of the present invention is preferably a biaxially oriented polyester film. Biaxial orientation in the present invention means a film that exhibits a biaxially oriented pattern in wide-angle X-ray diffraction. The polyester film can be obtained by stretching an unstretched (unoriented) film in two dimensions using a conventional method. Stretching can be performed using either sequential biaxial stretching or simultaneous biaxial stretching. Sequential biaxial stretching can involve stretching in the longitudinal direction (longitudinal) and the width direction (transverse), either once longitudinally and once transversely, or twice, e.g., longitudinal-transverse-longitudinal-transverse.

[0033] The polyester film of the present invention may contain inorganic particles, organic particles, or both, as long as the properties of the present invention are not impaired. Examples of inorganic particles include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, alumina (α-alumina, β-alumina, γ-alumina, δ-alumina), mica, mica titanium, zeolite, talc, clay, kaolin, lithium fluoride, calcium fluoride, montmorillonite, zirconia, wet silica, dry silica, and colloidal silica. Examples of organic particles include organic particles containing acrylic resins, styrene resins, silicone resins, and polyimide resins as components, and core-shell organic particles.

[0034] The thickness of the polyester film of the present invention is not particularly limited, but is preferably 10 μm to 300 μm, more preferably 12 μm to 100 μm, and even more preferably 14 μm to 50 μm. If the thickness is less than 10 μm, the film may not have sufficient rigidity, which may increase the frequency of film breakage during the film formation process. Furthermore, when the film is used as a molding substrate for MLCCs, uneven coating (uneven film thickness) may occur during the production of ceramic green sheets due to film breakage or film stretching.

[0035] The polyester film of the present invention may have a single-layer substrate, two-layer substrate, or three or more layers. In the case of a two-layer substrate, the substrate is composed of a polyester A layer and a polyester B layer. In the case of a three-layer substrate, the substrate is a laminate film composed of a polyester A layer, a polyester B layer, and a polyester C layer, or a three-layer substrate consisting of a polyester A layer, a polyester B layer, and a polyester A layer. In the case of a three-layer laminate film composed of an A layer / B layer / C layer or a A layer / B layer / A layer, the A layer is a layer suitable for forming a release layer or a surface onto which a release material is applied, the C layer is a layer suitable for forming the surface opposite the release layer, and the B layer is a layer located between the A layer and the C layer or between the A layer and the A layer (hereinafter sometimes referred to as an intermediate layer). Furthermore, the intermediate layer may contain pre-consumer materials generated from waste routes such as film edge portions generated during the film production process, recycled materials obtained by regenerating in-house recycled materials generated from waste routes of other film production processes, or post-consumer materials, as long as they do not adversely affect the properties of the film surface. The blending ratio may be such that the material is made up solely of recycled materials such as release films that are discarded after being used as products, or the recycled materials may be appropriately mixed with other raw materials, thereby achieving cost benefits.

[0036] Next, a method for producing the polyester film of the present invention will be explained, but the present invention should not be construed as being limited to the products obtained by such examples.

[0037] The polyester used in the present invention can be obtained by a conventional polymerization method. For example, it can be obtained by subjecting a dicarboxylic acid component such as terephthalic acid or its ester-forming derivative to a transesterification reaction or esterification reaction using a known method with a diol component such as ethylene glycol or its ester-forming derivative, followed by a melt polymerization reaction. If necessary, the polyester obtained by the melt polymerization reaction can be subjected to a solid-state polymerization reaction at a temperature below the melting point of the polyester.

[0038] The polyester film of the present invention can be obtained by a conventionally known production method, but by producing the film under the following conditions for the stretching and heat treatment steps, at least one side can be made to have a surface having the above-mentioned preferable physical properties.

[0039] The polyester film of the present invention contains the components represented by Structural Formulae 1 to 3. The components may be incorporated by any conventional method. In particular, adding the components represented by Structural Formulae 1 to 3 before the step of preparing the unstretched sheet may result in good dispersion of the components represented by Structural Formulae 1 to 3.

[0040] The polyester film of the present invention can be produced by a method (melt casting method) in which, if necessary, dried raw materials are heated and melted in an extruder, extruded through a die onto a cooled casting drum, and processed into a sheet. When a polyester film having two or more layers is produced by the melt casting method, an extruder is used for each layer constituting the polyester film, and the raw materials for each layer are melted and filtered through a filter. Because even very small foreign particles can cause large protrusion defects if they enter the polyester film, it is effective to use a high-precision filter that captures, for example, 95% or more of foreign particles 3 μm or larger. Subsequently, the molten raw materials are laminated in a merging device, introduced into a die, and extruded through the die onto a casting drum to form a sheet (co-extrusion method). The sheet is preferably cooled and solidified by static electricity on a drum cooled to a surface temperature of 20°C to 60°C, producing an unstretched sheet. The temperature of the casting drum is preferably 20°C to 40°C, and even more preferably 20°C to 30°C. If the temperature exceeds 60°C, the film may stick to the casting drum, making it difficult to obtain an unstretched sheet.

[0041] Next, when biaxially stretching an unstretched film, the conditions for longitudinal stretching are preferably such that the unstretched film is introduced into a group of rolls heated to 70°C or higher, stretched in the longitudinal direction, and then cooled with a group of rolls set at a temperature of 20°C to 50°C. The lower limit of the heating roll temperature during longitudinal stretching is not particularly limited as long as it does not impair the stretchability of the sheet. However, it is preferable that the heating roll temperature exceeds the glass transition temperature of the polyester resin used. Furthermore, the preferred range of the longitudinal stretching ratio is 3x to 5x, and a more preferred range is 3x to 4x. A longitudinal stretching ratio of 3x or more promotes orientation crystallization, improving film strength. On the other hand, a stretching ratio of 5x or less can prevent excessive orientation crystallization of the polyester resin during stretching, which can lead to embrittlement and tearing during film formation. A method using a speed difference between rolls is preferably used to stretch the film in the longitudinal direction. In this case, it is also a preferred embodiment to stretch the film in multiple sections while fixing the film with nip rolls to prevent the film from slipping. The stretching speed in the longitudinal direction is preferably 5,000% / min or more and 100,000% / min or less.

[0042] Next, for stretching in the direction perpendicular to the longitudinal direction (width direction), the film is introduced into a tenter while holding both ends with clips, and stretched in the direction perpendicular to the longitudinal direction (width direction) by 3 to 5 times in an atmosphere heated to a temperature of 70 to 160°C. The stretched film is then heat-treated to stabilize the internal orientation structure. The thermal history temperature of the film during heat treatment can be confirmed by the temperature of a small endothermic peak (sometimes referred to as Tmeta) that appears just below the melting point temperature measured with a differential scanning calorimeter (DSC) described below. When polyester (melting point 255°C) is the main component, the tenter temperature is preferably set so that the maximum temperature inside the tenter is 200 to 250°C. When other thermoplastic resins are the main component, it is preferably set to the resin melting point minus 5°C or less, i.e., the resin melting point minus 5°C or less. By setting the heat treatment temperature to 200°C or higher, the dimensional stability of the biaxially oriented polyester film can be improved, and by setting the heat treatment temperature to 250°C or lower, the occurrence of film breakage due to melting of the polyester film can be suppressed, allowing for efficient production. A more preferred range is 220°C or higher and 245°C or lower.

[0043] For the reasons mentioned above, the range of Tmeta, which represents the thermal history temperature of the film during heat treatment, is preferably 190°C or higher and 245°C or lower when the main component is polyester resin, and more preferably 210°C or higher and 240°C or lower.

[0044] Furthermore, in order to impart dimensional stability after the heat treatment, a relaxation treatment may be performed in the range of 1% to 6%. A relaxation treatment of 1% or more can improve the dimensional stability when the polyester film is used in a high-temperature environment, while a relaxation treatment of 6% or less can keep the polyester film under an appropriate tension, preventing thickness unevenness from worsening.

[0045] The stretching ratio is set to 3 to 5 times in both the longitudinal and transverse directions, with the area ratio (longitudinal stretching ratio × transverse stretching ratio) preferably being 9 to 22 times, more preferably 9 to 20 times. Setting the area ratio to 9 times or more promotes molecular orientation of the resulting polyester film and improves durability, while setting the area ratio to 22 times or less suppresses tearing during stretching. Furthermore, the stretching ratio (longitudinal stretching ratio / transverse stretching ratio) is preferably 0.6 to 1.7 times, more preferably 0.7 to 1.5 times, and even more preferably 0.8 to 1.3 times. Setting the stretching ratio to 0.6 to 1.7 times allows for control of the molecular orientation of the resulting polyester film, enabling uniform elongation even at temperatures above the glass transition temperature.

[0046] For example, when producing a release film, the polyester film of the present invention is coated with a release agent and cured by heat treatment. Because the polyester film shrinks and stretches due to the heat treatment and tension during transport, the polyester film of the present invention has little unevenness in the release layer and can be preferably used for release applications. Furthermore, the film of the present invention is provided with a release layer on at least one side, and can also be suitably used for appearance inspection purposes after a release layer is provided on the release layer. For example, This is because the defect position of the solid electrolyte can be detected accurately if the support is for use in producing a solid electrolyte for a battery. Note that the solid electrolyte also includes semi-solid electrolytes that contain liquid or gel-like substances.

[0047] <Characteristics evaluation method> A. Evaluation by pyrolysis GC / MS Approximately 100 μg of the sample is taken from the polyester film and freeze-pulverized to obtain a powdered sample, which is then subjected to pyrolysis GC / MS measurement under the following conditions. (Measuring equipment) Pyrolysis furnace:PY-3030iD GC:7890A MS:JMS-Q1050GC (Measurement conditions) Pyrolysis temperature: 600℃ Column: "Ultra ALLOY" (registered trademark)-5 (MS / HT) Heating conditions: Hold at 40°C for 3 minutes, then heat to 320°C at 20°C / min, and hold at 320°C for 18 minutes Mode: Split (20:1) 1.5mL / min constant flow Ionization method: EI+ Scan range: m / z 10,000-800,000 Scan speed: 0.5s / scan.

[0048] (i) Peak area per unit mass The peak area value per unit mass (au / μg) is calculated by dividing the sum of the peak area values ​​detected as structural formulas 1 to 3 by the mass of the sample used, assuming the maximum peak intensity of the obtained chromatogram to be 100. Here, the peak area value per unit mass is the arithmetic average value of the sample sampled at any two locations.

[0049] B. Evaluation by Emission Spectrum Measurement A polyester film is laid out and the emission spectrum is measured under the following conditions. The emission intensity is normalized by the excitation light intensity of each wavelength during the measurement. The wavelength dependency of the detection sensitivity of the spectrometer is also corrected, and dark count correction is also performed. (Measurement conditions) Equipment: Horiba Jobin Yvon Fluorolog 3-22 Light source: Xenon lamp Detector: PMT Excitation wavelength: 350 nm Observation wavelength: up to 750 nm (2 nm intervals) Excitation side slit width: 2 nm Observation side slit width: 2 nm Time constant: 0.2s Measurement mode: Sc / Rc Observation position: 22.5° to the excitation light (i) Emission peak intensity From the obtained emission spectrum, the emission peak intensity at each wavelength is determined.

[0050] (ii) Luminescent The value calculated by the following formula is taken as the luminescence. Luminescence = (I 550nm ) / (I 370nm ) x 100 Here, I 550nm is the emission peak intensity at 550 nm, I 370nm is the emission peak intensity at 370 nm. The luminescence properties are evaluated according to the following criteria. A: 15 or more B: 10 or more and less than 15 C: 5 or more but less than 10 D: Less than 5 C. Evaluation by thermostatic tensilon above the glass transition temperature The polyester film was cut into rectangular samples measuring 150 mm in length and 10 mm in width at random positions in the longitudinal and transverse directions. Using a tensile tester (Orientec "Tensilon" (registered trademark) UCT-100) with an initial tensile chuck distance of 50 mm and a tensile speed of 300 mm / min, a tensile test was performed in the longitudinal and transverse directions to determine the Young's modulus and elongation at break. The sample was placed in a thermostatic chamber set to 100°C and preheated for 90 seconds before the tensile test in air.

[0051] (i) Young's modulus The tensile Young's modulus is calculated from the tangent to the rising part of the obtained load-elongation curve. Measurements are carried out 10 times for each sample, and the average value obtained is used.

[0052] (ii) Breaking elongation The value calculated by the following formula is the breaking elongation. Elongation at break (%) = 100 × (L-L0) / L0 Here, L0 is the length of the sample before the test (mm), and L is the length of the sample at the time of fracture.

[0053] (iii) Elongation uniformity Elongation uniformity is evaluated by the coefficient of variation (standard deviation / average value) of breaking elongation. Measurements are taken 10 times for each sample, and the coefficient of variation of breaking elongation is calculated. The lower the coefficient of variation of breaking elongation, the less variation there is, which is preferable as it leads to improved accuracy in subsequent processes.

[0054] D. Atomic absorption spectrometry The alkali metal elements are quantified by atomic absorption spectrometry (Hitachi, Ltd.: Polarized Zeeman Atomic Absorption Spectrometer 180-80. Flame: acetylene-air).

[0055] E. Thickness of each layer When the polyester film is a laminated film, the thickness of each layer is measured by the following method: A cross section of the film is cut out with a microtome in a direction parallel to the width direction of the film, and the cross section is observed under a scanning electron microscope at 5000x magnification to measure the thickness of each laminated layer.

[0056] F. Intrinsic viscosity (IV) A measurement sample (polyester resin (raw material)) is dissolved in 100 ml of orthochlorophenol (solution concentration C (measurement sample weight / solution volume) = 1.2 g / 100 ml), and the viscosity of the solution at 25°C is measured using an Ostwald viscometer. The viscosity of the solvent is also measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] is calculated according to the following formula (1), and the obtained value is taken as the intrinsic viscosity (IV). ηsp / C=[η]+K[η] 2 ·C···(1) (Here, ηsp = (solution viscosity / solvent viscosity)-1, and K is the Huggins constant (assumed to be 0.343).) If the solution containing the measurement sample contains insoluble matter such as inorganic particles, the measurement is carried out using the following method. (1-1) Dissolve the measurement sample in 100 mL of orthochlorophenol to prepare a solution with a concentration of 1.2 g / 100 mL or more. The weight of the measurement sample added to the orthochlorophenol is the measurement sample weight. (1-2) Next, the solution containing the insoluble matter is filtered, and the weight of the insoluble matter and the volume of the filtrate after filtration are measured. (1-3) Add orthochlorophenol to the filtrate after filtration to adjust the ratio (weight of measured sample (g) - weight of insoluble matter (g)) / (volume of filtrate after filtration (mL) + volume of added orthochlorophenol (mL)) to 1.2 g / 100 mL. (For example, if a concentrated solution with a sample weight of 2.0 g and a solution volume of 100 mL is prepared and the weight of the insoluble matter when the solution is filtered is 0.2 g and the volume of the filtrate after filtration is 99 mL, then an adjustment is made by adding 51 mL of orthochlorophenol ((2.0 g - 0.2 g) / (99 mL + 51 mL) = 1.2 g / 100 mL).) (1-4) Using the solution obtained in (1-3), the viscosity at 25°C is measured using an Ostwald viscometer, and using the obtained solution viscosity and solvent viscosity, [η] is calculated according to the above formula (1), and the obtained value is taken as the intrinsic viscosity (IV).

[0057] G. Melting point of polyester film Tm (℃) The measurement sample is measured according to the method based on JIS K 7121 (1987) using a differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Instruments Inc. and a disk session "SSC / 5200" for data analysis, as follows:

[0058] 5 mg of sample is weighed into a sample pan and heated from 25°C to 300°C at a heating rate of 10°C / min to obtain a differential scanning calorimetry chart for the first run. The peak temperature of the endothermic peak in the differential scanning calorimetry chart for the first run is determined and designated as Tm (°C).

[0059] H. Pinhole evaluation Glass beads with a number-average particle size of 2 mm were added to 100 parts by weight of barium titanate (manufactured by Fuji Titanium Industries Co., Ltd., product name HPBT-1), 10 parts by weight of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., product name BL-1), 5 parts by weight of dibutyl phthalate, and 60 parts by weight of toluene-ethanol (30:30 by weight ratio), and the mixture was mixed and dispersed using a jet mill for 20 hours. The mixture was then filtered to prepare a dielectric paste. The resulting dielectric paste was applied to a release film using a die coater to a dry thickness of 2 μm, dried, and wound up to obtain a ceramic green sheet with a release film. The wound ceramic green sheet was unwound and visually inspected without being peeled from the release film to check for the presence or absence of pinholes. The observation area was 300 mm wide and 500 mm long. The ceramic green sheet molded on the release film was inspected for pinholes while illuminated from behind with a 1000 lux backlight unit, and evaluated as follows. A: There are three or fewer pinholes. B: 4 to 6 pinholes. C: 7 to 9 pinholes. D: 10 or more pinholes.

[0060] I. Particle size The average particle size is determined by the equivalent spherical diameter of the particle at the 50% volume point measured using an electron microscope photograph of the particle. The equivalent spherical diameter is the diameter of a sphere having the same volume as the particle.

[0061] J. Particle thermal decomposition temperature Using a Rigaku Denki TAS-100, measure the thermobalance weight loss curve at a temperature rise rate of 20°C / min in a nitrogen atmosphere. The temperature at which 10% weight loss occurs is taken as the thermal decomposition temperature. [Example]

[0062] The present invention will be described below with reference to examples, but the present invention is not necessarily limited to these examples.

[0063] [Production of PET-1] Terephthalic acid and ethylene glycol were polymerized using antimony trioxide and magnesium acetate tetrahydrate as catalysts in a conventional manner to obtain melt-polymerized PET. The resulting melt-polymerized PET-1 had a glass transition temperature of 81°C, a melting point of 255°C, an intrinsic viscosity of 0.65, and a terminal carboxyl group content of 20 eq. / t.

[0064] [Production of Particle A] Seed particles made of polystyrene were synthesized by emulsion polymerization of vinylbenzene and methacrylic acid using a conventional method. Emulsion polymerization of the seed particles with vinylbenzene, divinylbenzene, and methacrylic acid was then carried out using sodium peroxide as a polymerization initiator to obtain particles A, which consisted of a divinylbenzene-styrene crosslinked structure. The particle size of particles A was 0.4 μm, and the thermal decomposition temperature was 400°C.

[0065] [Preparation of Coating A] Coating agent A was obtained by mixing 100 parts by mass of an addition reaction type silicone resin release agent (manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name KS-847T) and 1 part by mass of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name CAT-PL-50T) in toluene as a solvent to give a solids content of 1.5% by mass.

[0066] [Preparation of dielectric paste] 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. under the trade name HPBT-1), 10 parts by mass of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd. under the trade name BL-1), 5 parts by mass of dibutyl phthalate, and 60 parts by mass of toluene-ethanol (mass ratio 30:30), and the mixture was mixed and dispersed in a jet mill for 20 hours, and then filtered to produce a dielectric paste.

[0067] Example 1 PET-1 was vacuum dried at 160°C for 2 hours, and then 0.10% by mass of each of the components represented by structural formulas 1 to 3 was added and stirred. The mixture was then placed in an extruder, melted at 280°C, and extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet.

[0068] The sheet was then preheated with a group of heated rolls, stretched 3.8 times in the longitudinal direction at 90°C, and then cooled with a group of rolls at 25°C to obtain a uniaxially stretched film. While holding both ends of the uniaxially stretched film with clips, it was stretched 4.0 times in the width direction perpendicular to the longitudinal direction in a heating zone at 100°C in a tenter. This was followed by heat setting at 230°C for 10 seconds in a heat treatment zone in the tenter. The film was then uniformly and slowly cooled in a cooling zone and wound up to obtain a polyester film with a thickness of 31 μm.

[0069] Coating agent A was applied to one side of the obtained polyester film by gravure coating so that the coating thickness after drying would be 100 nm, and a release film was obtained. A dielectric paste was applied to the obtained release film as the release material by die coating so that the thickness after drying would be 1.0 μm, and the film was dried and wound up to obtain a ceramic green sheet. The evaluation results are shown in the table.

[0070] [Production of PET-2] The polyester film obtained in Example 1 was pulverized into flakes using a grinder and then stirred in an aqueous alkali solution containing sodium as the alkali metal element for 5 minutes. The flakes were dried in a vacuum and then placed in a vented extruder. The pressure was maintained at a reduced pressure of 1 kPa or less, and the mixture was kneaded while removing moisture to obtain PET-2. PET-2 had a glass transition temperature of 78°C, a melting point of 253°C, an intrinsic viscosity of 0.60, and a terminal carboxyl group content of 37 eq. / t.

[0071] [Production of PET-3] The polyester film obtained in Example 1 was pulverized in a grinder to form flakes, which were then stirred in an aqueous alkali solution containing sodium as the alkali metal element for 2 minutes. The flakes were dried in a vacuum and then placed in a vented extruder. The pressure was maintained at a reduced pressure of 1 kPa or less, and the mixture was kneaded while removing moisture to obtain PET-3. PET-3 had a glass transition temperature of 79°C, a melting point of 253°C, an intrinsic viscosity of 0.60, and a terminal carboxyl group content of 38 eq. / t.

[0072] [Production of PET-4] PET-1 was vacuum dried at 160°C for 2 hours, then loaded into an extruder, melted at 280°C, and extruded through a die onto a casting drum at a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated using a group of heated rolls, stretched 3.8 times in the longitudinal direction at 90°C, and cooled using a group of rolls at 25°C to produce a uniaxially stretched film. The resulting uniaxially stretched film was held at both ends with clips and stretched 4.0 times in the width direction perpendicular to the longitudinal direction in a heating zone at 100°C in a tenter. Subsequently, the film was heat-set for 10 seconds at 230°C in a heat treatment zone in the tenter. The film was then uniformly cooled in a cooling zone and wound up to produce a 31 μm thick polyester film. The polyester film was pulverized into flakes in a grinder and vacuum-dried. It was then loaded into a vented extruder and kneaded while removing moisture at a reduced pressure of 1 kPa or less to produce PET-4. The glass transition temperature of PET-4 was 78°C, the melting point was 253°C, the intrinsic viscosity was 0.60, and the amount of terminal carboxyl groups was 39 eq. / t.

[0073] [Production of PET-5] PET-1 and Particle A were fed into a vented extruder so that the Particle A content was 1.0% by mass relative to the PET-5, and the mixture was kneaded while removing moisture under a reduced pressure of 1 kPa or less to obtain PET-5. The glass transition temperature was 81°C, the melting point was 255°C, the intrinsic viscosity was 0.61, and the amount of terminal carboxyl groups was 22 eq. / t.

[0074] [Production of PET-6] PET-6 was produced in the same manner as PET-4, except that PET-1 was replaced with PET-5. The glass transition temperature of PET-6 was 79°C, the melting point was 252°C, the intrinsic viscosity was 0.60, and the amount of terminal carboxyl groups was 28 eq. / t.

[0075] Examples 2 to 6 A polyester film was prepared in the same manner as in Example 1, except that the amounts of the components represented by Structural Formulas 1 to 3 added were changed as shown in the table.

[0076] Examples 7 to 12 Polyester films were produced in the same manner as in Examples 1 to 6, except that PET-1 was changed to PET-2.

[0077] Example 13 A polyester film was produced in the same manner as in Example 1, except that PET-1 was changed to PET-3.

[0078] (Comparative Example 1) A polyester film was prepared in the same manner as in Example 1, except that the components represented by Structural Formulas 1 to 3 were not added.

[0079] (Comparative Example 2) A polyester film was prepared in the same manner as in Comparative Example 1, except that PET-1 was changed to PET-4.

[0080] (Comparative Example 3) A polyester film was produced in the same manner as in Comparative Example 1, except that PET-1 was changed to PET-5.

[0081] Comparative Example 4 A polyester film was produced in the same manner as in Comparative Example 1, except that PET-1 was changed to PET-6.

[0082] (Comparative Example 5) A polyester film was prepared in the same manner as in Example 1, except that the amounts of the components represented by Structural Formulas 1 to 3 added were changed as shown in the table.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Table 3]

[0086] [Table 4]

[0087] In Examples 1 to 13, the peak area per unit mass in pyrolysis GC / MS evaluation was within a preferred range, and thus polyester films with excellent elongation uniformity and luminescence were obtained. In particular, in Examples 7 to 13, the components represented by Structural Formulas 1 to 3 were uniformly dispersed by contact with an aqueous solution containing an alkali metal element, resulting in excellent release layer coatability and excellent pinhole evaluation.

[0088] In Comparative Examples 1 to 4, the peak area value per unit mass in pyrolysis GC / MS evaluation was less than 150, so the film had poor elongation uniformity and poor luminescence. In Comparative Example 5, the peak area value per unit mass in pyrolysis GC / MS evaluation exceeded 2000, so the polyester film was prone to breakage and the elongation uniformity was uneven. [Industrial Applicability]

[0089] The polyester film of the present invention has excellent uniformity of elongation at temperatures above its glass transition temperature, allowing a release agent to be uniformly applied thereto, and is therefore suitable for use in mold release applications.Furthermore, the polyester film has excellent luminescence properties in response to excitation light of a specific wavelength, making it suitable for use in appearance inspection applications.

Claims

1. When pyrolysis gas chromatography mass spectrometry (pyrolysis GC / MS) was performed using the following measurement device and under the following measurement conditions, one or more of the following structural formulas 1 to 3 was detected: A polyester film having a peak area per unit mass detected as structural formulas 1 to 3 of 150 to 2000 a.u. / μg. 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 (Measuring device) Pyrolysis furnace: PY-3030iD GC: 7890A MS: JMS-Q1050GC (Measurement conditions) Thermal decomposition temperature: 600℃ Column: Ultra ALLOY-5 (MS / HT) Heating conditions: hold at 40°C for 3 minutes, then heat to 320°C at 20°C / min, and hold at 320°C for 18 minutes Inlet: 300℃ Mode: Split (20:1) 1.5 mL / min constant flow Ionization method: EI+ Scan range: m / z 10,000 to 800,000 Scan speed: 0.5 s / scan

2. 550 nm emission peak intensity (I ５５０ｎｍ ) and 370 nm emission peak intensity (I ３７０ｎｍ ) satisfies the following formula (i): (i)5≦(I ５５０ｎｍ ) / (I ３７０ｎｍ )×100≦20

3. 3. The polyester film according to claim 1, wherein the content of alkali metal elements in the polyester film is from 1.5 ppm by mass to 40.0 ppm by mass.

4. 3. The polyester film according to claim 1, wherein the alkali metal element contained in the polyester film is sodium.

5. 3. The polyester film according to claim 1, which is used for release purposes.

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