Laminated biaxially oriented polyester film for use in release film, and release film including said laminated biaxially oriented polyester film

Abstract

The purpose of the present invention is to provide a polyester film that is for use in a release film and that can suppress generation of protrusions and achieve a high level of breaking strength in the longitudinal direction of the polyester film serving as a base material. The present invention pertains to a laminated biaxially oriented polyester film for use in a release film, the polyester film comprising a surface layer on which a release layer is to be laminated, and a readily slidable layer containing lubricant particles and a polyester resin. The surface layer contains an antimony compound, an alkaline-earth metal compound, a phosphorus compound, and a polyester resin. The surface layer has a limiting viscosity of 0.55 dl / g or more. The antimony element content in the surface layer is 120 ppm or less.

Description

Laminated biaxially oriented polyester film for release film, and release film containing said laminated biaxially oriented polyester film

[0001] The present invention relates to a laminated biaxially oriented polyester film for use as a release film, and a release film comprising the laminated biaxially oriented polyester film.

[0002] The manufacture of multilayer ceramic chip capacitors (sometimes abbreviated as MLCC) includes a process for producing internal electrodes. The sheet method is the mainstream for this process. In the sheet method, a dielectric paste is applied to a release film (also called a carrier film) and dried to form a dielectric sheet, and internal electrodes are printed on the dielectric sheet. The internal electrodes are die-cut together with the dielectric sheet, and the sheet is peeled off from the release film and subjected to the next process for manufacturing a ceramic capacitor. Previously, the remaining release film was discarded. However, there has been a recent demand for the recycling of release films to reduce environmental impact, and release films suitable for recycling are being developed (Patent Document 1).

[0003] International Publication No. 2024 / 004832

[0004] A typical release film is composed of a polyester film substrate and a release layer laminated on the surface of the film. The release layer is the layer on which a dielectric paste is applied. A typical polyester film substrate has a three-layer structure, consisting of, from top to bottom, a surface layer, an intermediate layer, and an easy-slip layer. A release film is formed by laminating a release layer on the surface layer. Here, if there are many protrusions on the surface of the surface layer, convex portions will appear on the internal electrode printing surface through the release layer and the dielectric sheet layer, degrading the quality of the internal electrode. For this reason, it is necessary to minimize or eliminate the protrusions on the surface of the surface layer.

[0005] The inventors discovered that when the amount of antimony compound used in producing the surface layer was reduced, the formation of these protrusions was suppressed, but the longitudinal breaking strength of the polyester film used as the base material was reduced.

[0006] Based on this finding, further research was conducted and it was found that by reducing the amount of antimony compound used in producing the surface layer while extending the polymerization time or by additionally carrying out solid-state polymerization, it is possible to suppress the formation of protrusions and achieve high breaking strength in the longitudinal direction of the polyester film serving as the base material, thereby completing the present invention.

[0007] The present invention typically includes the following aspects: Item 1. A laminated biaxially oriented polyester film for use in a release film, having a surface layer onto which a release layer is to be laminated, and a lubrication layer containing lubricant particles and a polyester resin, wherein the surface layer contains an antimony compound, an alkaline earth metal compound, a phosphorus compound, and a polyester resin, the surface layer has an intrinsic viscosity of 0.55 dl / g or more, and the surface layer has an antimony element content of 120 ppm or less. Item 2. The number of protrusions containing antimony present on the surface of the surface layer is 0.020 / cm. ２ Item 3. The laminated biaxially oriented polyester film for a release film according to Item 1, wherein the number of particles filtered on a membrane filter by the following filtration method is less than or equal to 1 mm of the membrane filter. ２Item 1 or 2. The laminated biaxially stretched polyester film for release films according to Item 1 or 2, wherein the number of particles per kg of the surface layer is 400 or less. Filtration method: 10 g of a sample obtained by scraping the surface layer is dissolved in 80 ml of a p-chlorophenol / tetrachloroethane mixed solution to prepare a solution, and the solution is filtered under reduced pressure through a membrane filter having an average pore size of 0.5 μm. Here, the p-chlorophenol / tetrachloroethane mixed solution consists solely of p-chlorophenol and tetrachloroethane in a mass ratio of 3 parts p-chlorophenol to 1 part tetrachloroethane, and the membrane filter is made of polytetrafluoroethylene, has a circular shape with a diameter of 47 mm, and is 90 μm thick. Item 4. The laminated biaxially stretched polyester film for release films according to any one of Items 1 to 3, wherein the antimony element content of particles filtered on the membrane filter by the following filtration method is 10 mg or less per kg of the surface layer. Filtration method: 10 g of the sample obtained by scraping the surface layer is dissolved in 80 ml of a p-chlorophenol / tetrachloroethane mixed solution to prepare a solution, and the solution is filtered under reduced pressure through a membrane filter with an average pore size of 0.5 μm. Here, the p-chlorophenol / tetrachloroethane mixed solution consists solely of p-chlorophenol and tetrachloroethane in a mass ratio of 3 parts p-chlorophenol to 1 part tetrachloroethane, and the membrane filter is made of polytetrafluoroethylene, has a circular shape with a diameter of 47 mm, and is 90 μm thick. Item 5. The laminated biaxially stretched polyester film for a release film according to any one of Items 1 to 4, wherein the proportion of particles containing elemental antimony among the particles collected on the filter by the following filtration method is 30% or less. Filtration method: 10 g of the sample obtained by scraping the surface layer is dissolved in 80 ml of a p-chlorophenol / tetrachloroethane mixed solution to prepare a solution, and the solution is filtered under reduced pressure through a membrane filter with an average pore size of 0.5 μm. Here, the p-chlorophenol / tetrachloroethane mixed solution consisted only of p-chlorophenol and tetrachloroethane, with a mass ratio of p-chlorophenol to tetrachloroethane of 3:1, and the membrane filter was made of polytetrafluoroethylene, was circular with a diameter of 47 mm, and was 90 μm thick.Item 6. The laminated biaxially oriented polyester film for release films according to any one of Items 1 to 5, wherein the surface layer has an alkaline earth metal element content of 5 to 160 ppm and a phosphorus element content of 1 to 40 ppm. Item 7. The laminated biaxially oriented polyester film for release films according to any one of Items 1 to 6, wherein the surface layer has an intrinsic viscosity of 0.55 to 0.62 dl / g. Item 8. The laminated biaxially oriented polyester film for release films according to any one of Items 1 to 7, wherein the heat shrinkage rate in the longitudinal direction under heat conditions of 150°C for 30 minutes is 1.4% or less. Item 9. The laminated biaxially oriented polyester film for release films according to any one of Items 1 to 8, further comprising an intermediate layer between the surface layer and the lubricity layer. Item 10. Item 10. A release film comprising the laminated biaxially oriented polyester film for a release film according to any one of items 1 to 9 and a release layer, wherein the release layer is laminated on the surface layer of the laminated biaxially oriented polyester film.

[0008] According to the present invention, it is possible to provide a polyester film for use as a release film, which has a reduced number of protrusions on the surface layer and high breaking strength in the longitudinal direction.

[0009] As used herein, the phrase "comprising" is intended to encompass the phrases "consisting essentially of" and "consisting of."

[0010] In the numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in a certain stage can be arbitrarily combined with the upper or lower limit of a numerical range in the same stage or in another stage. In addition, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example.

[0011] In this specification, numerical values ​​connected with "to" mean a numerical range including the numerical values ​​before and after "to" as the lower and upper limits. For example, "1 to 10% by mass" is equivalent to "1% by mass or more and 10% by mass or less."

[0012] In this specification, with regard to a numerical range, "to" means equal to or greater than the leftmost numerical value and equal to or less than the rightmost numerical value. For example, "0.5 to 10% by mass" and "0.5% to 10% by mass" both mean "0.5% by mass or greater and 10% by mass or less." Furthermore, with regard to a numerical range, "equal to or greater than" means "the same as or greater than," and "equal to or less than" means "the same as or less than."

[0013] The release film can be composed of a polyester film as a base material (hereinafter also simply referred to as a base film) and a release layer laminated on the surface of the film. The laminated biaxially oriented polyester film of the present invention is a base film for a release film.

[0014] (Laminated biaxially oriented polyester film for release film) The substrate film of the present invention includes at least a surface layer (hereinafter also referred to as Layer A) and a lubricious layer (hereinafter also referred to as Layer B). The surface layer is one of the outermost layers of the substrate film, and the lubricious layer is the other outermost layer. In addition to the surface layer and the lubricious layer, the substrate film preferably includes an intermediate layer (hereinafter also referred to as Layer C) between the surface layer and the lubricious layer. Therefore, the layer structure in the thickness direction of the substrate film can be A / B or A / C / B. A release layer is formed on the surface layer to form a release film. Therefore, the layer structure in the thickness direction of the release film can be release layer / A / B or release layer / A / C / B. Since the intermediate layer is cheaper than the surface layer and the lubricious layer, the thickness of the surface layer and the lubricious layer can be reduced by including the intermediate layer, making the substrate film more inexpensive.

[0015] The thickness ratio of the surface layer may be 30% to 50% of the total layer thickness when an intermediate layer is provided and the layer structure in the thickness direction is A / C / B. When an intermediate layer is not provided and the layer structure in the thickness direction is A / B, it may be 50% to 90% of the total layer thickness, more preferably 70% to 90%. The thickness of the surface layer may be 3.6 μm to 50 μm, preferably 4.5 μm to 40 μm, more preferably 5 μm to 30 μm. The thickness ratio of the lubrication layer may be 10% to 30% of the total layer thickness when an intermediate layer is provided and the layer structure in the thickness direction is A / C / B. When an intermediate layer is not provided and the layer structure in the thickness direction is A / B, it may be 10% to 50% or 10% to 30% of the total layer thickness. The thickness of the lubrication layer may be 3.6 μm to 50 μm, preferably 4.5 μm to 40 μm, more preferably 4.5 μm to 10 μm. The thickness ratio of the intermediate layer may be 20% to 60% or 30% to 50% of the total layer thickness. The thickness of the intermediate layer may be 3.6 μm to 50 μm, preferably 4.5 μm to 40 μm, and more preferably 5 μm to 20 μm. The thickness of the base film may be 12 μm to 100 μm, preferably 15 μm to 80 μm, more preferably 15 μm to 50 μm, and even more preferably 15 μm to 35 μm. The film thickness is not particularly limited and can be measured by known methods, but can also be measured using an optical interference film thickness meter or by observing a cross section with a scanning electron microscope or transmission electron microscope.

[0016] The substrate film of the present invention is a laminated biaxially oriented polyester film for use as a release film, and includes a surface layer for laminating a release layer thereon, and a lubrication layer containing lubricant particles and a polyester resin. The surface layer contains an antimony compound, an alkaline earth metal compound, a phosphorus compound, and a polyester resin. The surface layer preferably has an intrinsic viscosity (intrinsic viscosity) of 0.55 dL / g or more. The surface layer preferably has an antimony element content of 120 ppm or less.

[0017] The antimony compound contained in the surface layer may be used alone or in combination of two or more. The antimony compound may be an antimony salt of an aliphatic carboxylic acid. The antimony salt of an aliphatic carboxylic acid may be antimony trioxide, antimony pentoxide, antimony acetate, etc., and antimony trioxide is preferred in terms of polycondensation reactivity, color tone of the resulting polymer, and inexpensive availability.

[0018] The content of the antimony compound in the surface layer may be an amount such that the elemental antimony content in the surface layer is 120 ppm or less, preferably 110 ppm or less, and more preferably 90 ppm or less. The content of the antimony compound in the surface layer may be 1 to 120 ppm, 1 to 110 ppm, 1 to 90 ppm, 10 to 120 ppm, 10 to 110 ppm, 10 to 90 ppm, 30 to 120 ppm, 30 to 110 ppm, 30 to 90 ppm, or the like. The elemental antimony content in the surface layer can be determined using an ICP optical emission analyzer. Specifically, it can be determined by the method described in the examples.

[0019] The alkaline earth metal compound contained in the surface layer may be used alone or in combination of two or more. The alkaline earth metal compound is preferably a magnesium compound. The magnesium compound may be an inorganic acid salt selected from saturated aliphatic carboxylates, unsaturated aliphatic carboxylates, aromatic carboxylates, halogen-containing carboxylates, hydroxycarboxylates, sulfates, nitric acid, phosphoric acid, phosphonic acid, hydrogen phosphate, hydrogen sulfide, sulfurous acid, thiosulfuric acid, hydrochloric acid, hydrobromic acid, chloric acid, and bromic acid, an organic sulfonate, an organic sulfate, a chelate compound, or an oxide. From the viewpoints of ease of handling and availability, saturated aliphatic carboxylates of magnesium metal are preferred, and magnesium acetate is more preferred.

[0020] The content of alkaline earth metal compounds in the surface layer may be an amount that results in an alkaline earth metal element content in the surface layer of 200 ppm or less, 160 ppm or less, 100 ppm or less, 80 ppm or less, 60 ppm or less, 5 to 200 ppm, 5 to 160 ppm, etc., with an amount of 5 to 100 ppm being preferred, an amount of 5 to 80 ppm being more preferred, an amount of 5 to 60 ppm being even more preferred, and an amount of 30 to 60 ppm being even more preferred. The content of alkaline earth metal elements in the surface layer can be determined using an ICP optical emission analyzer. Specifically, it can be determined by the method described in the examples.

[0021] The phosphorus compound contained in the surface layer can be used alone or in combination of two or more. Examples of the phosphorus compound include phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof, and specific examples include phosphoric acid, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphorous acid, trimethyl phosphite, tributyl phosphite, methylphosphonic acid, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl ethylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenyl phenylphosphonate, etc. Among these, trimethyl phosphate, diethyl ethylphosphonate, and / or phosphoric acid are preferred, and trimethyl phosphate is more preferred.

[0022] The content of the phosphorus compound in the surface layer may be an amount that results in an elemental phosphorus content in the surface layer of 50 ppm or less, 40 ppm or less, 30 ppm or less, etc., and is preferably an amount that results in an amount of 1 to 50 ppm, more preferably an amount that results in an amount of 1 to 40 ppm, even more preferably an amount that results in an amount of 1 to 30 ppm, and even more preferably an amount that results in an amount of 10 to 30 ppm.

[0023] The number of protrusions containing antimony present on the surface of the surface layer is 0.020 / cm ２ Below, 0.015 pieces / cm ２ Below, 0.012 pieces / cm ２ Below, 0.001 to 0.020 pieces / cm ２ , 0.001~0.015 pieces / cm ２ , 0.001~0.012 pieces / cm２ , 0.003~0.020 pieces / cm ２ , 0.003~0.015 pieces / cm ２ , 0.003~0.012 pieces / cm ２ etc., and may be 0.005 to 0.020 pieces / cm ２ is preferably 0.005 to 0.015 particles / cm ２ More preferably, 0.005 to 0.012 particles / cm ２ The number of protrusions containing elemental antimony is determined by observing the surface of the surface layer with a scanning white light interference microscope (magnification: 10x), processing the obtained microscopic image with surface analysis software VS-Viewer Version 10.0.3.0 built into the microscope, counting the number of protrusions with a height of 0.1 μm or more, and performing elemental analysis on the locations where protrusions with a height of 0.1 μm or more were measured with a digital microscope equipped with a laser analysis function to count the number of protrusions with a height of 0.1 μm or more in which antimony element was detected, and then multiplying the number of protrusions by the observation area (210 mm × 297 mm: area: approximately 623.7 cm). ２ ) can be obtained by dividing by the above formula. Specifically, it can be specified by the method described in the Examples.

[0024] The antimony element content in the surface layer may be 120 ppm or less. The antimony element content is preferably 110 ppm or less, and more preferably 90 ppm or less. The antimony element content in the surface layer may be 1 to 120 ppm, 1 to 110 ppm, 1 to 90 ppm, 10 to 120 ppm, 10 to 110 ppm, 10 to 90 ppm, 30 to 120 ppm, 30 to 110 ppm, 30 to 90 ppm, etc. The antimony element content in the surface layer can be determined using an ICP optical emission analyzer. Specifically, it can be determined by the method described in the examples.

[0025] The alkaline earth metal element content of the surface layer may be 200 ppm or less, 160 ppm or less, 100 ppm or less, 80 ppm or less, 60 ppm or less, 5 to 200 ppm, 5 to 160 ppm, etc., with 5 to 100 ppm being preferred, 5 to 80 ppm being more preferred, 5 to 60 ppm being even more preferred, and 30 to 60 ppm being even more preferred. The alkaline earth metal element may form foreign matter in the surface layer. The alkaline earth metal element content in the surface layer can be determined using an ICP optical emission analyzer. Specifically, it can be determined by the method described in the examples.

[0026] The phosphorus content of the surface layer may be 50 ppm or less, 40 ppm or less, 30 ppm or less, etc., preferably 1 to 50 ppm, more preferably 1 to 40 ppm, even more preferably 1 to 30 ppm, and even more preferably 10 to 30 ppm. The phosphorus content of the surface layer can be determined using an ICP emission spectrometer. Specifically, it can be determined by the method described in the examples.

[0027] The sample (10 g) obtained by scraping the surface layer was dissolved in a p-chlorophenol / tetrachloroethane mixed solution (80 ml), and the solution was filtered under reduced pressure through a membrane filter. The filter after filtration was dried, and the number of particles on the obtained dried filter was counted per 1 mm of the membrane filter. ２ Hereinafter, the solution will be simply referred to as the "solution solution" and the dry filter will be simply referred to as the "dry filter." The number of particles on the dry filter is calculated based on the number of particles per 1 mm of the membrane filter. ２The number of particles per dry filter is preferably 350 or less, more preferably 300 or less, and even more preferably 200 or less. Here, the p-chlorophenol / tetrachloroethane mixed solution consists solely of p-chlorophenol and tetrachloroethane, with a mass ratio of 3:1 for parachlorophenol:tetrachloroethane. The membrane filter has an average pore size of 0.5 μm, is made of polytetrafluoroethylene, is circular with a diameter of 47 mm, and is 90 μm thick. The membrane filter may be, for example, T050A047A manufactured by ADVANTEC. In the present invention, the number of such particles can be reduced by reducing the amount of antimony compound used in the manufacturing process of the polyester resin that constitutes the surface layer. The number of particles on the dry filter can be determined by observing the dry filter at 1,000x magnification using a scanning electron microscope (SEM). Specifically, it can be determined by the method described in the Examples.

[0028] The antimony element content of the particles filtered on the dry filter may be 10 mg or less per 1 kg of surface layer. The antimony element content is preferably 6 mg or less, more preferably 5 mg or less, and even more preferably 4 mg or less per 1 kg of surface layer. The antimony element content may be 0.1 to 10 mg, 0.1 to 6 mg, 0.1 to 5 mg, 0.1 to 4 mg, 1 to 10 mg, 1 to 6 mg, 1 to 5 mg, 1 to 4 mg, 2 to 10 mg, 2 to 6 mg, 2 to 5 mg, 2 to 4 mg, etc. per 1 kg of surface layer. The antimony element content of the particles filtered on the dry filter can be determined by measuring the particles on the dry filter with fluorescent X-rays to determine the amount of Sb element per 10 g of surface layer and converting this to the amount per 1 kg of polyester film. Specifically, it can be determined by the method described in the Examples.

[0029] The proportion of particles containing antimony among the particles collected on the dry filter may be 30% or less. The proportion of particles containing antimony among the particles on the dry filter is preferably 28% or less, more preferably 25% or less, and even more preferably 20% or less. The proportion of particles containing antimony among the particles on the dry filter may be 1 to 28%, 1 to 25%, 1 to 20%, 5 to 28%, 5 to 25%, 5 to 20%, 10 to 28%, 10 to 25%, 10 to 20%, etc. The proportion of particles containing antimony can be determined by performing elemental analysis of the particles on the dry filter using a scanning electron microscope (SEM) at a magnification of 1,000x, counting the number of particles in which Sb element is detected (Sb-containing particles), and dividing the number of particles in which Sb element is detected by the total number of particles on the dry filter to calculate the proportion (%) of the number of Sb-containing particles. Specifically, it can be determined by the method described in the Examples.

[0030] The number of particles collected on the dry filter is ２ The number of particles collected on the dry filter may be 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 200 or less per mm of the filter. ２ The number of particles collected on the dry filter may be 1 to 500, 1 to 400, 1 to 350, 1 to 200, 10 to 500, 10 to 400, 10 to 350, 10 to 200, 50 to 500, 50 to 400, 50 to 350, 50 to 200, 100 to 500, 100 to 400, 100 to 350, 100 to 200, etc. per particle. The number of particles collected on the dry filter can be determined by observing the dry filter at 1,000x magnification using a scanning electron microscope (SEM) and counting the number of particles. Specifically, it can be determined by the method described in the Examples.

[0031] The intrinsic viscosity of the surface layer and the base film may each be 0.55 dl / g or more. The intrinsic viscosity can be controlled by adjusting the polymerization conditions (polymerization time, addition of solid-state polymerization, etc.) of the polyester resin constituting the surface layer. The intrinsic viscosity may be 0.56 dl / g or more, 0.57 dl / g or more, 0.58 dl / g or more, 0.55 to 0.62 dl / g, 0.56 to 0.62 dl / g, 0.57 to 0.62 dl / g, or 0.58 to 0.62 dl / g. An intrinsic viscosity within the above range is advantageous in that the breaking strength of the base film is increased and the heat shrinkage rate of the base film is reduced. The intrinsic viscosity can be determined in accordance with JIS K 7367-5 by measuring a sample obtained by scraping the surface layer or a substrate film using a mixed solvent of phenol (6 parts by mass) and 1,1,2,2-tetrachloroethane (4 parts by mass) at a temperature of 30° C. Specifically, the intrinsic viscosity can be determined by the method described in the examples.

[0032] The heat shrinkage rate in the longitudinal direction of the base film under heat conditions of 150°C for 30 minutes may be 1.4% or less. The heat shrinkage rate in the longitudinal direction can be controlled by adjusting the intrinsic viscosity of the polyester resin constituting the surface layer. The heat shrinkage rate in the longitudinal direction is preferably 1.0% or less, and more preferably 0.9% or less. The heat shrinkage rate in the longitudinal direction may be 0.1 to 1.4%, 0.1 to 1.0%, 0.1 to 0.9%, 0.2 to 1.4%, 0.2 to 1.0%, 0.2 to 0.9%, 0.5 to 1.4%, 0.5 to 1.0%, 0.5 to 0.9%, etc. When the heat shrinkage rate in the longitudinal direction is within the above range, the dimensional stability at high temperatures is excellent. In the manufacture of capacitor internal electrodes, a conductive paste is applied to a release film, dried to form a conductive layer, and then the internal electrodes are printed on the conductive layer. Therefore, the low thermal shrinkage of the base film at high temperatures contributes to suppressing the thermal shrinkage of the release film, etc., and makes it easier to print and form the internal electrodes with high precision. The thermal shrinkage in the longitudinal direction can be determined by heat-treating a base film 10 mm wide and 220 mm long in a hot air oven at 150°C for 30 minutes and comparing the longitudinal dimensions before and after the heat treatment. Specifically, it can be determined by the method described in the examples.

[0033] The longitudinal breaking strength of the base film may be 170 MPa or more, 180 MPa or more, or 190 MPa or more. The breaking strength is preferably 170 to 300 MPa, more preferably 180 to 280 MPa, and even more preferably 190 to 260 MPa. A longitudinal breaking strength within the above range is advantageous in that defects such as cracking, tearing, bending, and ripping are less likely to occur during the processing and use of the base film. The longitudinal breaking strength can be determined by measurement in accordance with JIS K 7127. Specifically, it can be determined by the method described in the examples.

[0034] The surface layer may be a film made of a polyester resin (preferably polyethylene terephthalate). Therefore, the surface layer may contain a polyester resin (preferably polyethylene terephthalate). The content of the polyester resin in the surface layer may be 70 to 100% by mass, 80 to 100% by mass, etc., preferably 90 to 100% by mass, and more preferably 95 to 100% by mass.

[0035] The polyester resin, which is the raw material for the surface layer, can be produced by a direct polymerization method in which dicarboxylic acid and glycol are directly reacted; a transesterification method in which an alkyl ester of dicarboxylic acid (e.g., a dialkyl ester (e.g., dimethyl ester, diethyl ester, dibutyl ester)) is subjected to a transesterification reaction with a glycol, followed by polycondensation; or a method in which a diglycol ester of dicarboxylic acid is polycondensed. For example, polyethylene terephthalate can be produced by producing an oligomer mixture such as bis(2-hydroxyethyl) terephthalate through an esterification reaction or transesterification reaction between terephthalic acid or dimethyl terephthalate and ethylene glycol, and then melt-polymerizing this mixture at high temperature under vacuum using a catalyst. In addition, the molten polymer can be solid-phase polymerized at a temperature below the melting point. By performing solid-phase polymerization after melt polymerization, it is possible to increase the intrinsic viscosity and lower the acid value while suppressing the generation of foreign matter with a major axis of 1 μm or more and antimony-based foreign matter (particles containing elemental antimony).

[0036] The dicarboxylic acids may be used singly or in combination of two or more. The dicarboxylic acids may be aromatic dicarboxylic acids, aliphatic dicarboxylic acids, etc., with aromatic dicarboxylic acids being preferred.

[0037] The aromatic dicarboxylic acid may be terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid (e.g., 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid), 4,4'-biphenyldicarboxylic acid, 4,4'-biphenylsulfonedicarboxylic acid, 4,4'-biphenyletherdicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, pamoic acid, anthracenedicarboxylic acid, or the like, with terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid being preferred, and terephthalic acid being more preferred.

[0038] The aliphatic dicarboxylic acid may be a saturated aliphatic dicarboxylic acid such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, or dimer acid; or an unsaturated aliphatic dicarboxylic acid such as fumaric acid, maleic acid, or itaconic acid.

[0039] The diols may be used singly or in combination of two or more. The diols may be aliphatic glycols, aromatic glycols, etc., with aliphatic glycols being preferred.

[0040] Diols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, 1,10-decamethylene glycol, and 1,12-dodecanediol. aliphatic glycols such as polyethylene glycol, polytrimethylene glycol, and polytetramethylene glycol; and aromatic glycols such as hydroquinone, 4,4'-dihydroxybisphenol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-bis(β-hydroxyethoxyphenyl)sulfone, bis(p-hydroxyphenyl)ether, bis(p-hydroxyphenyl)sulfone, bis(p-hydroxyphenyl)methane, 1,2-bis(p-hydroxyphenyl)ethane, bisphenol A, bisphenol C, 2,5-naphthalenediol, and glycols obtained by adding ethylene oxide to these glycols, with ethylene glycol being preferred.

[0041] The surface layer may be a polyethylene terephthalate film, a polytrimethylene terephthalate film, a polybutylene terephthalate film, or a polyethylene-2,6-naphthalate film, with a polyethylene terephthalate film being preferred. Accordingly, the polyester resin constituting the surface layer may be polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, or polyethylene-2,6-naphthalate, with a polyethylene terephthalate being preferred.

[0042] The polyester resin constituting the surface layer is preferably a polyester resin whose main dicarboxylic acid component is terephthalic acid or a polyester resin whose main diol component is ethylene glycol, and more preferably a polyester resin whose main dicarboxylic acid component is terephthalic acid and whose main diol component is ethylene glycol (polyethylene terephthalate).

[0043] Here, the term "main dicarboxylic acid component" means that, when the total dicarboxylic acid components in the polyester resin is taken as 100 mol%, the dicarboxylic acid or its ester component accounts for 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 100 mol%.

[0044] Furthermore, the term "main diol component" can mean that, when the total diol components in the polyester resin are 100 mol%, the diol component is 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 100 mol%.

[0045] A polymerization catalyst may be used in melt polymerization to produce a polyester resin. The polymerization catalyst may be used alone or in combination of two or more. An antimony compound is preferred as the polymerization catalyst. The antimony compound may be used alone or in combination of two or more. The antimony compound may be an antimony salt of an aliphatic carboxylic acid. The antimony salt of an aliphatic carboxylic acid may be antimony trioxide, antimony pentoxide, or antimony acetate. Antimony trioxide is preferred in terms of polycondensation reactivity, the color tone of the resulting polymer, and inexpensive availability. Examples of catalysts other than antimony compounds include alkaline earth metal compounds, manganese compounds, cobalt compounds, aluminum compounds, titanium compounds, titanium / silicon composite oxides, and germanium compounds. Catalysts other than antimony compounds may be used to the extent that they do not cause problems with the properties of the surface layer.

[0046] When producing a polyester resin, it is preferable to add an alkaline earth metal. The alkaline earth metal compound can be used alone or in combination of two or more. The alkaline earth metal compound is preferably a magnesium compound. The magnesium compound may be an inorganic acid salt selected from saturated aliphatic carboxylates, unsaturated aliphatic carboxylates, aromatic carboxylates, halogen-containing carboxylates, hydroxycarboxylates, sulfates, nitric acid, phosphoric acid, phosphonic acid, hydrogen phosphate, hydrogen sulfide, sulfurous acid, thiosulfuric acid, hydrochloric acid, hydrobromic acid, chloric acid, and bromic acid, an organic sulfonate, an organic sulfate, a chelate compound, or an oxide of magnesium metal. From the viewpoints of ease of handling and availability, saturated aliphatic carboxylates of magnesium metal are preferred, and magnesium acetate is more preferred.

[0047] When producing a polyester resin, it is preferable to add a phosphorus compound as a heat stabilizer. The phosphorus compounds may be used alone or in combination of two or more. Examples of phosphorus compounds include phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples include phosphoric acid, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphorous acid, trimethyl phosphite, tributyl phosphite, methylphosphonic acid, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl ethylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, and diphenyl phenylphosphonate. Among these, trimethyl phosphate, diethyl ethylphosphonate, and / or phosphoric acid are preferred, and trimethyl phosphate is more preferred.

[0048] When producing the polyester resin, various compounds and additives may be added within the range that does not cause problems in the properties of the surface layer obtained from the polyester resin.

[0049] An example of the production of a polyester resin constituting a surface layer is as follows. The polyester resin below is polyethylene terephthalate. The present invention may be a method for producing a biaxially stretched polyester film for a surface layer constituting a release film, comprising the following steps 1 to 3.

[0050] [Step 1] A step of melt-polymerizing a polyester resin using terephthalic acid as the dicarboxylic acid component, ethylene glycol as the diol component, and an antimony compound as the main polymerization catalyst. [Step 2] Optionally, a step of solid-state polymerizing the polyester resin obtained in Step 1 at 200 to 240°C (preferably 197 to 225°C) for 5 to 10 hours (preferably 5 to 9 hours), preferably at 20 to 60 Pa, to obtain a polyester resin. [Step 3] A step of stretching the polyester resin obtained in Step 1 or 2 to obtain a biaxially stretched polyester film for use as a surface layer constituting a release film.

[0051] The melt polymerization may be a batch polymerization method or a continuous polymerization method. In either method, the esterification reaction or transesterification reaction may be carried out in one stage, but is preferably carried out in multiple stages. In the melt polymerization reaction, the number and size of reactors and the production conditions for each step can be selected as appropriate without any limitations. The melt polymerization reaction may be carried out in one stage or in multiple stages, preferably in two to five stages, more preferably in three to four stages, and even more preferably in three stages. The melt polymerization reaction is preferably carried out in a continuous reactor. A continuous reactor is a method in which a reaction vessel for the esterification reaction or transesterification reaction and a melt polymerization reaction vessel are connected by piping, and raw materials are continuously introduced into each reaction vessel without emptying, transferred to the melt polymerization reaction vessel via the piping, and the resin is withdrawn from the melt polymerization reaction vessel.

[0052] The steps of the continuous polymerization method are as follows.

[0053] 1) Slurry Preparation Step A dicarboxylic acid component and a diol component are introduced into a slurry preparation tank to prepare a slurry. The content ratio of these components in the slurry is not particularly limited as long as the slurry has sufficient fluidity to be transported to an esterification reaction tank. From an economical viewpoint, it is preferable to reuse the diol component recovered in the polycondensation step as a slurry raw material. In the present invention, recycled raw materials such as dicarboxylic acid components and diol components obtained by a chemical decomposition and recovery method may also be used.

[0054] 2) Esterification Reaction Step: The slurry obtained above is introduced into two or more esterification reaction vessels connected in series and subjected to an esterification reaction to obtain an oligomer compound in which a diol is condensed with both terminal carboxyl groups of a dicarboxylic acid component. The esterification reaction is preferably carried out while removing water produced by the reaction from the system using a distillation column. The number and size of the reaction vessels in the esterification reaction step can be selected as appropriate without any limitations. The production conditions for each step can be selected as appropriate depending on the type and amount of the polycondensation catalyst and additives for improving electrostatic adhesion, the number and size of the reaction vessels, etc. For example, in a system having three esterification reaction vessels, the temperature of the first esterification reaction vessel can be 240 to 270°C, the pressure can be 100 to 160 kPa absolute, and the average residence time can be 2 to 5 hours. When solid-state polymerization is not used, the average residence time is preferably 3.5 to 5 hours, more preferably 3.9 to 5 hours. The temperature of the second and third esterification reaction vessels may be 250 to 280°C, the pressure may be 0 to 100 kPa absolute, and the average residence time may be 0.1 to 2.5 hours. When solid-state polymerization is not used, the average residence time of the second esterification reaction is preferably 1.4 to 2.5 hours, more preferably 1.5 to 2.5 hours, and the average residence time of the third esterification reaction is preferably 1.0 to 2.5 hours, more preferably 1.1 to 2.5 hours. It is desirable that the final esterification reaction rate reaches 60% or more, preferably 70% or more. Furthermore, the esterification reaction vessel may be a multi-stage vessel provided with a weir or the like inside.

[0055] In the esterification step, it is preferable to additionally supply the diol component after the second esterification reaction vessel. Supplying the entire amount of the diol component in the slurry preparation can cause problems such as fluctuations in the diol component composition in the polyester resin and a decrease in the esterification reaction rate during long-term continuous production. By additionally supplying the diol component after the second esterification reaction vessel, these problems can be suppressed.

[0056] In the esterification step, a phosphorus compound, an alkali metal compound, an alkaline earth metal compound, etc. may be added. The timing of addition may be any time from before the esterification reaction to the start of the polycondensation reaction, but in the continuous polymerization method, it is preferable to add them in the third esterification reaction tank or later.

[0057] When producing a polyester resin by a batch polymerization method or a continuous polymerization method, the antimony compound may be added as a powder, an ethylene glycol slurry, an ethylene glycol solution, etc., but it is preferably added as an ethylene glycol solution. The addition time may be either before the esterification reaction and the ester exchange reaction, or between the end of the ester exchange reaction and the esterification reaction and the start of the polycondensation reaction.

[0058] 3) Polycondensation Reaction Step The oligomer compound that has undergone the esterification reaction is subsequently transferred to a polycondensation reaction tank and subjected to the polycondensation reaction. The number and size of the reaction tanks in the polycondensation reaction step are not limited and can be selected appropriately. Furthermore, the production conditions for each step can be selected appropriately depending on the type and amount of the polycondensation catalyst and additives, the number and size of the reaction tanks, and the like. For example, when three polycondensation reaction tanks are used, the temperature of the first polycondensation reaction tank can be 260 to 290°C, the pressure can be 2 to 8 kPa, and the average residence time can be 0.1 to 1 hour. When solid-state polymerization is not used, the average residence time of the first polycondensation reaction is preferably 0.8 to 1 hour, more preferably 0.9 to 1 hour. The temperature of the second polycondensation reaction tank can be 270 to 290°C, the pressure can be 0.5 to 1.5 kPa, and the average residence time can be 0.1 to 2 hours. When solid-state polymerization is not used, the average residence time for the second polycondensation is preferably 1.0 to 2 hours, more preferably 1.1 to 2 hours. The temperature of the third polycondensation reaction vessel may be 270 to 290°C, the pressure may be 0.01 to 0.5 kPa, and the average residence time may be 0.1 to 2 hours. When solid-state polymerization is not used, the average residence time for the third polycondensation is preferably 1.0 to 2 hours, more preferably 1.1 to 2 hours. It is preferable that the degree of increase in intrinsic viscosity achieved in each of these polycondensation reaction steps be smoothly distributed. Since the diol component is distilled in the polycondensation reaction step, it is preferable to recover, purify, and reuse it. This recovery and purification can be carried out in a distillation column, as in the esterification reaction step.

[0059] The intrinsic viscosity of the polyester resin produced by melt polymerization is preferably 0.52 to 0.59 dl / g, more preferably 0.52 to 0.56 dl / g. When the intrinsic viscosity of the polyester resin is within the above range, it is advantageous in that the generation of foreign matter is suppressed.

[0060] It is preferable to further subject the polyester resin obtained by melt polymerization to solid-state polymerization, since this reduces the number of protrusions containing antimony and increases the longitudinal breaking strength of the substrate film.

[0061] The solid state polymerization can be carried out on a polyester resin in the form of granules, which means chips, pellets, flakes, or powder, preferably pellets.

[0062] Solid-state polymerization can be carried out by heating the granular polyester resin at a temperature below the melting point of the polyester resin under an inert gas flow or under reduced pressure. The solid-state polymerization is preferably carried out under reduced pressure. The solid-state polymerization process may be carried out in one stage or in multiple stages. The granular polyester resin to be supplied to the solid-state polymerization process is preferably first heated to a temperature lower than the temperature used for solid-state polymerization to crystallize it, and then supplied to the solid-state polymerization process. The crystallization process is preferably carried out by heating the granular polyester at a temperature of 70 to 90°C for 3 to 5 hours to dry it, and then heating it at a temperature of typically 120 to 200°C, preferably 130 to 150°C, for 1 to 4 hours. After the crystallization process, the solid-state polymerization is preferably carried out at a temperature of 200 to 240°C and a pressure of 20 to 60 Pa for 5 to 9 hours.

[0063] 4) Stretching Process The polyester resin is stretched to form a film. Stretching can improve chemical resistance, heat resistance, mechanical strength, and other properties. The polyester resin for the surface layer, the polyester resin for the lubrication layer, and, if the substrate film has an intermediate layer, the polyester resin for the intermediate layer are co-extruded to form a two- or three-layer laminate sheet. Alternatively, each polyester resin is molded into a sheet (e.g., the polyester resin is melt-extruded into a sheet at 250 to 320°C and then solidified), and these sheets are then laminated together to form a two- or three-layer laminate sheet, which is then stretched. The substrate film can be obtained by stretching the laminate sheet. Stretching can be performed by known methods. For example, the laminate sheet can be biaxially stretched sequentially or simultaneously in the machine and cross directions at 70 to 140°C, followed by heat treatment at 160 to 240°C to obtain the substrate film. Typically, the stretching ratios in the longitudinal (machine direction) and transverse (width direction) directions can be selected from the range of 1.1 to 10 times, with the longitudinal stretching ratio being preferably 2.5 to 5.0 times, more preferably 2.8 to 5.0 times, and even more preferably 3.0 to 5.0 times. The width direction stretching ratio is preferably 2.5 to 5.0 times, more preferably 2.8 to 5.0 times, and even more preferably 3.0 to 5.0 times. A stretching ratio within the above range is advantageous in that thickness unevenness in the resulting substrate film is suppressed and the substrate film has excellent heat resistance and mechanical strength. Note that the stretching ratio defined in the present invention refers to the actual stretching ratio at which the substrate film is actually stretched. This stretching ratio can be determined by measuring the mass change per unit area before and after each stretching step or by marking a grid-shaped stretching ratio marker on the unstretched film.

[0064] The surface layer may contain particles, but from the viewpoint of reducing the surface layer's irregularities, it is preferable not to contain particles (especially particles with an average particle diameter of 1.0 μm or more). When particles are contained in the surface layer, examples of the particles include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. The particles may be of one type alone or a combination of two or more types. Titanium oxide, calcium carbonate, and silica, which are highly versatile, are preferred as particles. The average particle diameter of the particles is preferably 1 nm or more and less than 1.0 μm.

[0065] The substrate film may have a lubrication layer as the outermost layer on the side opposite the surface layer. The lubrication layer contains lubricant particles and a polyester resin. The lubrication layer may be a film made of a polyester resin (preferably made of polyethylene terephthalate). The lubrication layer may contain lubricant particles and a polyester resin (preferably polyethylene terephthalate). The content of the polyester resin in the lubrication layer may be 70 to 90% by mass, 80 to 90% by mass, 70 to 95% by mass, 80 to 95% by mass, 90 to 95% by mass, 70 to 100% by mass, 80 to 100% by mass, 90 to 100% by mass, 95 to 100% by mass, etc.

[0066] The lubrication layer may be a biaxially stretched polyethylene terephthalate film, polytrimethylene terephthalate film, polybutylene terephthalate film, or polyethylene-2,6-naphthalate film, with polyethylene terephthalate film being preferred. Therefore, the polyester resin constituting the lubrication layer may be polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, or polyethylene-2,6-naphthalate, with polyethylene terephthalate being preferred. A crosslinking agent may be used in combination with the polyester resin to further strengthen the layer. In this case, known crosslinking agents such as isocyanate resins and melamine resins can be used.

[0067] Examples of lubricant particles contained in the lubrication layer include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. From the viewpoint of the lubricating properties of the film and ease of air escape, the lubricant particles are preferably at least one type of particles selected from calcium carbonate particles or silica particles.

[0068] The lower limit of the particle size of the lubricant particles contained in the lubricating layer is preferably 0.2 μm, more preferably 0.3 μm, and even more preferably 0.4 μm. A particle size of 0.2 μm or more is preferable because it satisfies the slipperiness and prevents the occurrence of winding slippage. The upper limit of the particle size of the lubricant particles in the lubricating layer is preferably 5.0 μm, more preferably 4.0 μm, and even more preferably 3.0 μm. A particle size of 5.0 μm or less can reduce the surface roughness of the lubricating layer, preventing the risk of significant surface roughness being transferred to the release layer. The particle size of the lubricant particles can be 0.2 to 5.0 μm, 0.2 to 4.0 μm, 0.2 to 3.0 μm, 0.3 to 5.0 μm, 0.3 to 4.0 μm, 0.3 to 3.0 μm, 0.4 to 5.0 μm, 0.4 to 4.0 μm, or 0.4 to 3.0 μm.

[0069] The content of the lubricant particles contained in the lubrication layer may be 5,000 to 15,000 ppm, 3,000 to 15,000 ppm, or 5,000 to 10,000 ppm.

[0070] The lubrication layer may contain a surfactant to improve leveling during coating and to defoam the coating solution. The surfactant may be any of cationic, anionic, and nonionic surfactants, but silicone, acetylene glycol, and fluorine-based surfactants are preferred. These surfactants are preferably contained in the coating layer to an extent that excessive addition does not cause abnormalities in the coating appearance.

[0071] The lubrication layer can be formed by film formation by a known method on the surface layer when the layer structure is A / B, or on the intermediate layer when the layer structure is A / C / B. As the film formation method, for example, conventionally known methods such as coextrusion and lamination can be used. In addition, the surface layer and the lubrication layer can also be formed by applying the coating liquid for forming the surface layer and the coating liquid for forming the lubrication layer to the intermediate layer using a multilayer coater die or the like.

[0072] The substrate film may or may not have an intermediate layer between the surface layer and the lubricious layer.

[0073] A polyester resin may be used for the intermediate layer. To reduce the cost of the base film, a resin obtained by recycling a polyester film (e.g., a release film) may be used. When using a recycled resin, the proportion of the resin in the polyester resin is preferably 5 to 50% by mass. The intermediate layer may be a film made of a biaxially stretched polyester resin (preferably polyethylene terephthalate). The intermediate layer may contain a polyester resin (preferably polyethylene terephthalate). The content of the polyester resin in the intermediate layer may be 70 to 90% by mass, 80 to 90% by mass, 70 to 95% by mass, 80 to 95% by mass, 90 to 95% by mass, 70 to 100% by mass, 80 to 100% by mass, 90 to 100% by mass, 95 to 100% by mass, or the like.

[0074] The polyester resin constituting the intermediate layer is not particularly limited, and a film of a polyester resin commonly used as an intermediate layer in a release film can be used. A crystalline linear saturated polyester composed of an aromatic dibasic acid component and a diol component is preferred. For example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or a copolymer primarily composed of these resin components is even more preferred. Polyester films formed from polyethylene terephthalate are particularly preferred. The polyethylene terephthalate preferably contains 90 mol% or more, more preferably 95 mol% or more, of ethylene terephthalate repeating units, and may be copolymerized with small amounts of other dicarboxylic acid components or diol components. From a cost perspective, polyethylene terephthalate produced solely from terephthalic acid and ethylene glycol is preferred. Furthermore, known additives, such as antioxidants, light stabilizers, UV absorbers, and crystallization agents, may be added within limits that do not impair the effects of the substrate film.

[0075] (Release Film) The release film of the present invention comprises a laminated biaxially oriented polyester film (substrate film) for the release film of the present invention and a release layer, and has a structure in which the release layer is laminated on the surface layer of the laminated biaxially oriented polyester film. The release film of the present invention can be used in the production of resin sheets that require high smoothness, such as semiconductor parts, ceramic green sheets, and optical films, and is preferably used for printing internal electrodes of multilayer ceramic chip capacitors.

[0076] The release layer may be a release layer used in conventional release films. The release layer contains, for example, an acid-modified polyolefin resin and a crosslinking agent. Here, the acid-modified polyolefin resin is a copolymer containing an olefin unit and an unsaturated carboxylic acid unit as copolymerization components.

[0077] The acid-modified component constituting the acid-modified polyolefin resin may be an unsaturated carboxylic acid component. Examples of the unsaturated carboxylic acid component include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, crotonic acid, etc., as well as half esters and half amides of unsaturated dicarboxylic acids. Among these, from the viewpoint of dispersion stability of the resin, acrylic acid, methacrylic acid, maleic acid, and maleic anhydride are preferred, and acrylic acid, methacrylic acid, and maleic anhydride are particularly preferred. Two or more of these acid-modified components may be contained in the acid-modified polyolefin resin.

[0078] The acid-modified polyolefin resin must contain an olefin component as the main component. The olefin component is not particularly limited, but is preferably an alkene having 2 to 6 carbon atoms, such as ethylene, propylene, isobutylene, 2-butene, 1-butene, 1-pentene, or 1-hexene. A mixture of these may also be used. Among these, an alkene having 2 to 4 carbon atoms, such as ethylene, propylene, isobutylene, or 1-butene, is more preferred, with ethylene and propylene being even more preferred, and ethylene being most preferred.

[0079] The acid-modified polyolefin resin may be copolymerized with a small amount of other monomers, such as dienes, (meth)acrylonitrile, vinyl halides, vinylidene halides, carbon monoxide, and sulfur dioxide.

[0080] The components constituting the acid-modified polyolefin resin may be copolymerized in the acid-modified polyolefin resin in any form, including, for example, random copolymerization, block copolymerization, and graft copolymerization (graft modification).

[0081] Examples of acid-modified polyolefin resins include the Nucrel (registered trademark) series, which is an acid-modified polyolefin resin manufactured by DuPont-Mitsui Polychemicals, and the Rexpearl series, which is an acid-modified polyethylene resin manufactured by Japan Polyethylene Corporation.

[0082] Examples of acid-modified polyolefin resins containing an ethylenically unsaturated component containing an oxygen atom in the side chain include the Bondine (registered trademark) series, which is a maleic anhydride-modified polyolefin resin manufactured by Arkema Inc. Specific product names of the Bondine (registered trademark) series include "LX-4110," "HX-8210," "HX-8290," and "TX-8030."

[0083] The crosslinking agent may be a self-crosslinking agent, a compound having a plurality of functional groups reactive with a carboxyl group in the molecule, etc. Among these, isocyanate compounds, melamine compounds, urea compounds, epoxy compounds, carbodiimide compounds, oxazoline group-containing compounds, etc. are preferred, and among these, isocyanates are more preferred, and blocked isocyanates are most preferred.

[0084] The release layer can be formed by applying a coating liquid containing the raw materials for the release layer onto the surface layer and drying it. For example, it is preferable to apply a coating liquid containing an acid-modified polyolefin resin and a crosslinking agent onto the surface layer material and dry it. The coating liquid is preferably diluted with an organic solvent for better coatability.

[0085] Examples of organic solvents include: (1) alcohols such as methyl alcohol, ethyl alcohol, N-propyl alcohol, isopropyl alcohol, N-butyl alcohol, tridecyl alcohol, cyclohexyl alcohol, and 2-methylcyclohexyl alcohol; (2) glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and glycerin; (3) ethylene glycol monomethyl ether, ethylene glycol monoethylene ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol butyl ether; (3) glycol ethers such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl acetate, ethylene glycol monobutyl acetate, diethylene glycol monomethyl acetate, diethylene glycol monoethyl acetate, and diethylene glycol monobutyl acetate; (4) esters such as ethyl acetate, isopropylene acetate, and N-butyl acetate; (5) ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, isophorone, and diacetone alcohol; and (6) aromatic compounds such as benzene, toluene, and xylene. These can be used alone or in combination of two or more.

[0086] More preferably, the solvent of aromatic compounds, which has excellent solubility for acid-modified polyolefin resins, is contained in an amount of 20% by mass to 80% by mass of all organic solvents used in the coating solution. The other organic solvents are preferably selected taking into consideration leveling properties and drying properties. Furthermore, the boiling point of the organic solvent is preferably 60°C to 180°C. A boiling point of 60°C or higher is preferred because the solids concentration of the coating solution is less likely to change during coating, making it easier to stabilize the coating thickness. Conversely, a boiling point of 180°C or lower makes it easier to reduce the amount of organic solvent remaining in the coating film, making it preferred from the viewpoint of stability over time.

[0087] If there is a risk of foreign matter or undissolved matter of 1 μm or more being present in the coating liquid, it is preferable to remove them using a filter or the like before coating, from the viewpoint of the appearance after coating. Various types of filters can be suitably used, but it is preferable to use one that can remove 99% or more of particles of 1 μm in size. When a coating liquid from which foreign matter or undissolved matter of 1 μm or more has been removed is applied and dried, it is preferable because this can prevent the occurrence of depressions on the surface of the release layer.

[0088] The solid content concentration of the release agent contained in the coating liquid is preferably 0.1% by mass or more and 10% by mass or less. When the solid content concentration is 0.1% by mass or more, the drying time after application can be shortened, which is preferable from the viewpoint of productivity, and the amount of solvent remaining in the coating film is small, which is also preferable from the viewpoint of stability over time. On the other hand, when the solid content concentration is 10% by mass or less, the viscosity of the coating liquid does not become too high, which is preferable because satisfactory leveling properties can be obtained and sufficient flatness can be obtained. The viscosity of the coating liquid is preferably 10 cps or more and 300 cps or less from the viewpoint of coating appearance, and it is preferable to adjust the solid content concentration, organic solvent, etc. so that it falls within this range.

[0089] As a method for laminating a release layer on a surface layer of a transparent substrate by a coating method, commonly used methods such as gravure coating, kiss coating, dip coating, spray coating, curtain coating, air knife coating, blade coating, reverse roll coating, bar coating, and lip coating can be applied. Among these, gravure coating, which can apply uniformly, is preferred, and reverse gravure coating is particularly preferred. In addition, the gravure diameter is preferably 80 mm or less. If it is 80 nm or less, it is preferred because it can suppress the occurrence of ridges in the flow direction.

[0090] The lower limit of the release layer thickness is preferably 15 nm, more preferably 30 nm. A thickness of 15 nm or more is preferable because it provides sufficient release properties. The upper limit of the release layer thickness is preferably 150 nm, more preferably 120 nm. A thickness of 150 nm or less is preferable from the viewpoint of not only preventing deformation of the release layer and increasing surface roughness due to transfer, but also maintaining appropriate slip properties on the coated surface, and is also preferable from the viewpoint of winding quality, etc. The release layer thickness may be 15 to 150 nm, 15 to 120 nm, 30 to 150 nm, 30 to 120 nm, etc.

[0091] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Methods for determining various physical properties in the examples will be described below.

[0092] (Quantitative Determination of Sb, Mg, and P Elements in the Surface Layer) A sample (0.5 g) obtained by scraping the surface layer was dissolved in 15 ml of 60% nitric acid and 2 ml of ultrapure water to prepare a measurement sample. The contents (ppm) of Sb, Mg, and P relative to the mass of the polyester film were then determined using an ICP optical emission spectrometer (5900 ICP OES, manufactured by Agilent).

[0093] (Number of protrusions (Sb protrusions) containing antimony present on the surface of the surface layer) The substrate film was cut into a size conforming to the standard base paper size of A4 size (210 mm x 297 mm: area approximately 623.7 cm) of the Japanese Industrial Standards. ２) was cut out to prepare a sample, and the entire area of ​​this sample was visually inspected for foreign matter using the crossed Nicols method. Next, each foreign matter location detected in the sample was measured from the surface of the surface layer of the sample using a scanning white light interference microscope (device: "VertScan" (registered trademark) VS1540 manufactured by Hitachi High-Tech Science Corporation) using a 10x objective lens in Phase mode. The obtained microscopic image was subjected to image processing using the surface analysis software VS-Viewer Version 10.0.3.0 built into the microscope under the following conditions to obtain the height of the foreign matter location on the surface of the surface layer. (Image processing conditions) Image processing was performed in the following order. Interpolation processing: complete interpolation Filter processing: Gaussian (cutoff 100) Surface correction: 4th order

[0094] Furthermore, particle analysis processing was performed under the following conditions, and the number of particles displayed on the "Particle Analysis" screen detected at a height threshold of 25 nm (height threshold setting value: 0.025 μm) was counted. (Particle analysis conditions) Protrusion analysis processing was performed under the following conditions. Analysis type: Protrusion analysis Image correction: None Processing height threshold: 0.025 μm Reference height: Zero plane (average plane)

[0095] Of the protrusions (foreign matter) detected in this analysis, the presence or absence of antimony element was measured by the following component analysis for those portions of the surface layer where protrusions having a height of 0.1 μm or more were observed.

[0096] (Component Analysis of Protrusions) Elemental analysis was performed on the areas where protrusions with a height of 0.1 μm or more were observed using a digital microscope (VHX, manufactured by KEYENCE Corporation) equipped with a laser elemental analysis head (EA-300, manufactured by KEYENCE Corporation), and the number of protrusions (Sb protrusions) in which antimony element (Sb element) was detected was counted. The counted number was calculated based on the surface observation area (210 mm × 297 mm: area approximately 623.7 cm). ２ ) and calculate the 1 cm ２ The number of protrusions containing elemental antimony per unit area was calculated.

[0097] (Solution of Surface Layer) A sample (10 g) obtained by scraping off the surface layer was washed with water and dried, and then dissolved in a p-chlorophenol / tetrachloroethane mixed solution (a solution consisting only of parachlorophenol and tetrachloroethane in a mass ratio of 3 parts p-chlorophenol to 1 part tetrachloroethane) to obtain a solution.

[0098] (Filtration of the solution of the surface layer) The solution of the surface layer was filtered through a membrane filter (PTFE membrane filter manufactured by Advantec, product number: T050A430A), and the filtered filter was dried to obtain a dried filter. The membrane filter was made of polytetrafluoroethylene, had an average pore size of 0.5 μm, and was a circular filter with a diameter of 47 mm (147.6 mm ２ ) and its thickness was 90 μm.

[0099] (Number of Total Particles Collected by Filtration of Dissolution Solution) The dried filter was observed at a magnification of 1,000 times using a scanning electron microscope (SEM), and the number of particles was counted.

[0100] (Number of antimony-containing particles collected by filtration of solution and their proportion to the total number of particles) Elemental analysis was performed on the particles on the dry filter using a scanning electron microscope (SEM) at a magnification of 1,000 times, and the number of particles in which Sb element was detected (Sb-containing particles) was counted. The number of particles in which Sb element was detected was divided by the number of all particles to calculate the proportion (%) of the number of Sb-containing particles.

[0101] (Amount of Sb element in particles collected by filtration of solution) The particles on the dry filter were measured by fluorescent X-ray to determine the amount of Sb element per 10 g of the surface layer, which was converted into the amount (mg) per kg of the surface layer.

[0102] (Intrinsic viscosity of surface layer and base film) The intrinsic viscosity (dl / g) was measured in accordance with JIS K 7367-5 using a sample obtained by scraping the surface layer or the base film and a mixed solvent of phenol (6 parts by mass) and 1,1,2,2-tetrachloroethane (4 parts by mass) at a temperature of 30°C.

[0103] (Longitudinal Heat Shrinkage of Base Film) The base film was sampled to a size of 10 mm in the transverse direction and 220 mm in the longitudinal direction. Reference lines were marked on the sample at 200 mm intervals in the longitudinal direction, and the interval between the reference lines (L0) was measured. The sample was then sandwiched between sheets of paper and placed in a hot air oven controlled at a temperature of 150°C. After 30 minutes of treatment, the sample was removed and the interval between the reference lines (L) was measured. The heat shrinkage was calculated using the following formula: Heat shrinkage (%) = {(L0 - L) / L0} x 100

[0104] (Breaking Strength of Substrate Film) Breaking strength is the stress required to break the substrate film. Specifically, a tensile force is gradually applied to the substrate film, and the force at which the substrate film breaks is determined. This is expressed as a value (unit: MPa) converted into stress per unit area. Breaking strength was measured in accordance with JIS K 7127, specifically by the following method. That is, a film test piece having a width of 12.7 mm and a length of 200 mm was sampled, and the film test piece was set in a tensile tester (e.g., AG-X manufactured by Shimadzu Corporation). The film test piece was elongated at a chuck distance of 100 mm and a take-up speed of 100 mm / min under an environment of a temperature of 23°C and a humidity of 65% RH. The breaking strength was calculated from the measured values ​​of the elongation at break of the film test piece and the load required for breakage.

[0105] (Surface evaluation of substrate film as a release film used in the manufacture of multilayer ceramic chip capacitors (MLCCs)) The number of Sb protrusions on the surface of the surface layer was 0.015 / cm ２ Substrate films with this number or less were judged to have passed, and are marked with "Good" in Table 3. On the other hand, those that did not satisfy this condition were judged to have failed, and are marked with "Poor" in Table 4. Failure can increase the frequency of unevenness occurring on the printed surface when the substrate film is wound onto the roller, or when the internal electrodes are printed.

[0106] (Strength evaluation of base film as release film used in manufacturing multilayer ceramic chip capacitors (MLCC)) Base films having a longitudinal heat shrinkage rate of 1.4% or less and a breaking strength of 180 MPa or more were judged to pass, and are indicated by "◯" in Table 3. On the other hand, those not meeting these conditions were judged to fail, and are indicated by "×" in Table 3. Failure may result in breakage, cracking, etc. during production or use of the base film, or significant dimensional change may occur during heating when using the base film to form a dielectric sheet and internal electrodes.

[0107] (Overall evaluation of substrate films as release films used in the manufacture of multilayer ceramic chip capacitors (MLCCs)) When a film was evaluated as passing in both the surface evaluation and strength evaluation, the overall evaluation was deemed to be passing, and this was indicated by "◯" in Table 4. On the other hand, when a film was evaluated as failing in either or both of the surface evaluation and strength evaluation, this was deemed to be failing in the overall evaluation, and this was indicated by "×" in Table 4.

[0108] Example 1 <Production of Polyester Resin (Melt Polymerization)> (Slurry Preparation) A slurry was prepared by continuously feeding terephthalic acid and ethylene glycol in a ratio of 46.4 parts by mass of ethylene glycol to 100 parts by mass of terephthalic acid into a slurry preparation tank while stirring under nitrogen flow.

[0109] (Esterification Reaction) A continuous esterification reactor consisting of a three-stage complete mixing vessel equipped with a stirrer, a distillation column, a raw material inlet, and a product outlet was used as the esterification reactor. An ethylene glycol solution of antimony trioxide (antimony trioxide concentration: 12 g / L) was supplied to the first esterification reactor together with the prepared slurry, and the esterification reaction was carried out at an absolute pressure of 126 kPa, a temperature of 258°C, and an average residence time of 3.3 hours. The reaction liquid was withdrawn from the first esterification reactor so that the liquid level remained constant, and then introduced into the second esterification reactor. Ethylene glycol was introduced into the second esterification reactor through another inlet at an average rate of 230 kg / hour, and the esterification reaction was carried out at atmospheric pressure, a temperature of 261°C, and an average residence time of 1.3 hours. The reaction liquid was withdrawn from the second esterification reactor so that the liquid level remained constant, and then introduced into the third esterification reactor. In the third esterification reaction tank, an ethylene glycol solution containing magnesium acetate, an ethylene glycol solution containing sodium acetate, and an ethylene glycol solution containing trimethyl phosphate were each fed in equal amounts through separate inlets, and an esterification reaction was carried out at a temperature of 260°C under atmospheric pressure for an average residence time of 0.9 hours.

[0110] (Polycondensation Reaction) The reaction solution was removed from the third esterification reaction tank so that the liquid level remained constant, and then introduced into the first polycondensation reaction tank of a three-stage continuous polycondensation reaction apparatus, where the first polycondensation reaction was carried out at a pressure of 5.6 kPa, a temperature of 278°C, and an average residence time of 0.7 hours. The reaction solution was removed from the first polycondensation reaction tank so that the liquid level remained constant, and then introduced into the second polycondensation reaction tank. The second polycondensation reaction was carried out at a pressure of 0.75 kPa, a temperature of 282°C, and an average residence time of 0.9 hours. The reaction solution was removed from the second polycondensation product so that the liquid level remained constant, and then introduced into the third polycondensation reaction tank. The degree of vacuum (pressure) was adjusted so that the intrinsic viscosity of the reaction product was 0.53 dl / g at a temperature of 282°C and an average residence time of 0.9 hours. The pressure was in the range of 0.08 to 0.15 kPa. The polyester resin obtained through the above process was extruded into a strand shape, cooled in water, and then cut into pellets.

[0111] <Production of Polyester Resin 1 (Melt Polymerization and Solid-State Polymerization)> The polyester resin obtained by melt polymerization was charged into a solid-state polymerization apparatus. After drying at 90°C for 3.5 hours, it was crystallized at 130°C for 4.5 hours. The temperature was then gradually increased from 197°C to 220°C, and solid-state polymerization was carried out at a pressure of 40 Pa for 7 hours to obtain Polyester Resin 1 having an intrinsic viscosity of 0.617 dL / g.

[0112] <Production of Polyester Resins 2 to 6> Polyester Resins 2 to 6 were obtained in the same manner as Polyester Resin 1, except that the supply amount of the ethylene glycol solution of antimony trioxide was changed so as to achieve the Sb content (ppm) shown in Table 3, the esterification reaction time and polycondensation reaction time were changed to those shown in Table 2, and solid-state polymerization was not performed.

[0113] <Production of Recycled PET1> A used PET film having a silicone-based release layer on one side and containing 600 ppm of calcium carbonate with a particle size of 1.0 μm was placed in a single-screw grinder and pulverized using a 4 mm aperture screen at a rate of 100 kg / h to obtain a pulverized film. The pulverized film was then fed into a twin-screw extruder to obtain Recycled PET1. The intrinsic viscosity of Recycled PET1 was 0.56 dl / g and the Si concentration was 200 ppm.

[0114] <Production of Polyethylene Terephthalate / Calcium Carbonate Masterbatch (MB1)> The above polyester resin 4 and calcium carbonate particles having an average particle size of 1.0 μm were melt-kneaded in a twin-screw extruder to prepare a masterbatch with a calcium carbonate particle concentration of 20,000 ppm.

[0115] Example 1: Polyester resin 1, recycled PET1, and MB1 were dried and then melted at 285°C. Using separate melt extruders (290°C), each melt was subjected to two-stage filtration: one through a filter made of sintered stainless steel fibers with a 95% cut diameter of 15 μm, and the other through a filter made of sintered stainless steel particles with a 95% cut diameter of 15 μm. The filtered melts were then merged in a feed block to form a surface layer (Layer A), a lubricity layer (Layer B), and an intermediate layer (Layer C). The resulting sheet was extruded (cast) at a speed of 45 m / min, electrostatically bonded on a casting drum at 30°C, and cooled to obtain an unstretched laminated polyethylene terephthalate sheet (laminated PET sheet) with an intrinsic viscosity of 0.56 dl / g. In this case, the A layer was formed using only polyester resin 1, the B layer was formed using a blend of 75% by mass of polyester resin 1 and 25% by mass of MB1, and the C layer was formed using a blend of 60% by mass of polyester resin 1 and 40% by mass of recycled PET1. The layer thickness ratio was adjusted to A layer / C layer / B layer = 40% / 40% / 20% based on the output of each extruder. The electrostatic adhesion conditions were as follows: electrode material was tungsten, cylindrical (wire) with a diameter of 0.2 mm and a length of 0.5 m, current was constant at 5 mA, electrode tension was 5 kg, and electrode renewal speed was 5 m / hour.

[0116] The unstretched laminated PET sheet was then heated with an infrared heater and stretched 3.5 times in the machine direction at a roll temperature of 80°C using the speed difference between the rolls. It was then introduced into a tenter and stretched 4.2 times in the transverse direction at 140°C. It was then heat-treated at 210°C in a heat-setting zone. It was then relaxed 2.3% in the transverse direction at 170°C to obtain a mill roll (5.0 m wide) of a 25 μm-thick laminated biaxially oriented polyethylene terephthalate film (laminated biaxially oriented PET film).

[0117] The resulting mill roll was transferred to a slitter, processed with a static eliminator (Kasuga Electric Co., Ltd., high-density static elimination system) and a web cleaner (Shinkosha, ultrasonic cleaner system), and then cut to a width of 1,400 mm. A core material with an inner diameter of 6 inches, a wall thickness of 12 mm, a moisture content of 8%, a surface roughness (SRa = 4.3 nm, SRp = 41.4 nm), and a flattening compressive strength of 200 kg / 100 mm and a resin-impregnated paper was attached. A length of 8,000 m was wound at a maximum speed of 400 m / min using a contact roll with a rubber hardness of 60 degrees, under a contact surface pressure of 200 kg / m and a tension of 15 MPa, to obtain a laminated biaxially oriented PET film roll. A laminated biaxially oriented PET film (substrate film) was cut from the resulting roll and subjected to various evaluations. The evaluation results are shown in Tables 3 and 4.

[0118] Examples 2 to 5 and Comparative Examples 1 to 3 Laminated biaxially stretched PET films were produced in the same manner as in Example 1, except that the layer structure, layer thickness ratio, and constituent resin types and ratios of layers A to C were changed as shown in Table 1, and subjected to various evaluations. The evaluation results are shown in Tables 3 and 4.

[0119]

[0120]

[0121]

[0122]

[0123] The substrate films using polyester resins 1 to 3 in the surface layer showed excellent results in both the surface evaluation and the strength evaluation (Examples 1 to 5), and it was confirmed that they are suitable as release sheets useful for forming a dielectric sheet and printing internal electrodes in the manufacture of MLCCs. On the other hand, the substrate films using polyester resins 4 to 6 in the surface layer showed insufficient performance in either the surface evaluation or the strength evaluation, and were unable to achieve both surface performance and strength performance (Comparative Examples 1 to 3), and it was confirmed that there is significant room for improvement as release sheets used in forming a dielectric sheet and printing internal electrodes in the manufacture of MLCCs.

Claims

1. A laminated biaxially oriented polyester film for use in a release film, having a surface layer for laminating a release layer thereon, and an easy-slip layer containing lubricant particles and a polyester resin, wherein the surface layer contains an antimony compound, an alkaline earth metal compound, a phosphorus compound, and a polyester resin, the intrinsic viscosity of the surface layer is 0.55 dl / g or more, and the antimony element content of the surface layer is 120 ppm or less.

2. The number of protrusions containing antimony present on the surface of the surface layer is 0.020 / cm ２ The laminated biaxially oriented polyester film for a release film according to claim 1, wherein:

3. The number of particles filtered on the membrane filter by the following filtration method is ２ The laminated biaxially oriented polyester film for use as a release film according to claim 1 or 2, wherein the number of particles per particle is 400 or less. Filtration method: A 10 g sample obtained by scraping the surface layer is dissolved in 80 ml of a p-chlorophenol / tetrachloroethane mixed solution to prepare a solution, and the solution is filtered under reduced pressure through a membrane filter having an average pore size of 0.5 μm. Here, the p-chlorophenol / tetrachloroethane mixed solution consists solely of p-chlorophenol and tetrachloroethane in a mass ratio of 3 parts p-chlorophenol to 1 part tetrachloroethane, and the membrane filter is made of polytetrafluoroethylene, is circular, has a diameter of 47 mm, and is 90 μm thick.

4. The laminated biaxially oriented polyester film for use as a release film according to any one of claims 1 to 3, wherein the antimony element content of particles collected on a membrane filter by the following filtration method is 10 mg or less per 1 kg of the surface layer. Filtration method: 10 g of a sample obtained by scraping the surface layer is dissolved in 80 ml of a p-chlorophenol / tetrachloroethane mixed solution to prepare a solution, and the solution is filtered under reduced pressure through a membrane filter with an average pore size of 0.5 μm. Here, the p-chlorophenol / tetrachloroethane mixed solution consists solely of p-chlorophenol and tetrachloroethane in a mass ratio of 3 parts p-chlorophenol to 1 part tetrachloroethane, and the membrane filter is made of polytetrafluoroethylene, is circular, has a diameter of 47 mm, and is 90 μm thick.

5. The laminated biaxially oriented polyester film for use as a release film according to any one of claims 1 to 4, wherein the proportion of particles containing elemental antimony among particles collected on a filter by the following filtration method is 30% or less. Filtration method: 10 g of a sample obtained by scraping the surface layer is dissolved in 80 ml of a p-chlorophenol / tetrachloroethane mixed solution to prepare a solution, and the solution is filtered under reduced pressure through a membrane filter with an average pore size of 0.5 μm. Here, the p-chlorophenol / tetrachloroethane mixed solution consists solely of p-chlorophenol and tetrachloroethane in a mass ratio of 3 parts p-chlorophenol to 1 part tetrachloroethane, and the membrane filter is made of polytetrafluoroethylene, is circular, has a diameter of 47 mm, and is 90 μm thick.

6. The laminated biaxially oriented polyester film for use as a release film according to any one of claims 1 to 5, wherein the surface layer has an alkaline earth metal element content of 5 to 160 ppm and a phosphorus element content of 1 to 40 ppm.

7. The laminated biaxially oriented polyester film for use as a release film according to any one of claims 1 to 6, wherein the surface layer has an intrinsic viscosity of 0.55 to 0.62 dl / g.

8. A laminated biaxially oriented polyester film for release films according to any one of claims 1 to 7, which has a thermal shrinkage rate in the longitudinal direction of 1.4% or less under heat conditions of 150°C for 30 minutes.

9. The laminated biaxially oriented polyester film for use as a release film according to any one of claims 1 to 8, further comprising an intermediate layer between the surface layer and the lubricious layer.

10. A release film comprising the laminated biaxially oriented polyester film for use in a release film according to any one of claims 1 to 9 and a release layer, wherein the release layer is laminated on the surface layer of the laminated biaxially oriented polyester film.

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