Release film

Abstract

Provided is a release film having a polyester film base material and a release layer, wherein: the surface layer of the base material comprises a polyester containing an antimony compound, an alkaline earth metal compound, and a phosphorus compound; the intrinsic viscosity of the surface layer is 0.55 or more; the antimony atom content of the surface layer is 120 ppm or less; the surface free energy of the surface of the release layer is 18-35 mJ / m2; the thickness of the release layer is 50-1500 nm, the mean roughness (Sa) of an area of the surface of the release layer is 7 nm or less; and the maximum protrusion height is in the range of 100 nm or less.

Description

Release film

[0001] The present invention relates to a release film for molding resin sheets, and more particularly to a release film used when molding thin resin sheets.

[0002] Conventionally, release films, which use a polyester film as a base material and laminate a release layer on top of it, have been used as process films for molding resin sheets such as adhesive sheets, cover films, polymer films, and optical lenses. Furthermore, in recent years, there has been a demand for release films used in the manufacture of semiconductor products. In addition, release films are also in demand for use as release films in the manufacture of ceramic green sheets.

[0003] The aforementioned release film is also used as a process film for molding ceramic green sheets, which require high smoothness for multilayer ceramic capacitors, ceramic substrates, and other applications. In recent years, with the miniaturization and increase in capacitance of multilayer ceramic capacitors, there has been a trend towards thinner ceramic green sheets. Ceramic green sheets are molded by coating a slurry containing ceramic components such as barium titanate and a binder resin onto a release film and drying it. After printing electrodes onto the molded ceramic green sheet and peeling it off the release film, the ceramic green sheets are laminated, pressed, fired, and external electrodes are applied to manufacture a multilayer ceramic capacitor.

[0004] When molding a ceramic green sheet onto the surface of a polyester film substrate's release layer, the wettability and smoothness of the release film during ceramic slurry application, as well as the peelability when removing the ceramic green sheet from the release film, become crucial. Poor smoothness can lead to problems such as pinhole formation, uneven thickness, and sheet defects in the ceramic green sheet obtained after slurry application and drying.

[0005] In recent years, ceramic green sheets have become thinner, and there is a growing demand for ceramic green sheets with a thickness of 1.0 μm or less, more specifically, 0.2 μm to 1.0 μm. As a result, the requirements for smoothness in release films have increased even further.

[0006] Similarly, when using a flexible resin film as a dielectric in a film capacitor process, poor smoothness can lead to problems such as pinhole formation, uneven thickness, and sheet defects in the resin sheet.

[0007] As a release film with excellent smoothness, Patent Document 1 specifies that the number of protrusions of 1 μm or more is 1 per meter. ２ A release film is disclosed, characterized in that a release layer is provided on the following film.

[0008] Furthermore, Patent Document 2 discloses a method for manufacturing a biaxially oriented polyester film, characterized by lateral stretching in a stent oven where the number of dust particles is below a certain number.

[0009] Japanese Patent Publication No. 2007-237497 Japanese Patent Publication No. 2009-012242

[0010] However, the technology described in Patent Document 1 is a technique for suppressing protrusions of 1 μm or more, and in recent ceramic green sheets with a thickness of 0.2 μm to 1.0 μm, it is necessary to suppress protrusions that are shorter in height than before.

[0011] Furthermore, the biaxially oriented polyester film described in Patent Document 2 requires essential cleaning of the inside and outside of the coating machine and the stent oven. The number of protrusions on the film produced before cleaning is high, and the number of protrusions may vary depending on the location and cleaning conditions. Moreover, the protrusions that can be reduced by cleaning are limited to those caused by PET chips and foreign matter from disturbances adhering to or incorporated into the release layer surface. It is impossible to reduce the protrusions present in the polyester film substrate itself.

[0012] The inventors discovered that reducing the amount of antimony compound used during the manufacturing of the surface layer of a polyester film substrate suppresses the formation of protrusions on the surface of the polyester film substrate.

[0013] Based on these findings, further research revealed that by reducing the amount of antimony compound used in the production of the polyester film substrate surface layer, while adjusting the polymerization time or performing additional solid-phase polymerization, it is possible to suppress the formation of protrusions and achieve high longitudinal breaking strength and low thermal shrinkage stability of the polyester film substrate. This led to the completion of the present invention.

[0014] The present invention typically encompasses the following embodiments: [1] A release film having a polyester film substrate and a release layer, wherein the polyester film substrate comprises a surface layer (surface layer A) and a smooth-slip layer (surface layer B) containing polyester resin and lubricant particles, wherein the surface layer is made of polyester containing an antimony compound, an alkaline earth metal compound and a phosphorus compound, the intrinsic viscosity of the surface layer is 0.55 or more, the antimony atom content of the surface layer is 120 ppm or less, and the surface free energy of the surface of the release layer is 18 to 35 mJ / m ２ A release film having a release layer thickness of 50 nm to 1500 nm, a regional average surface roughness (Sa) of the surface of the release layer of 7 nm or less, and a maximum protrusion height of 100 nm or less. [2] The number of antimony element-containing protrusions present on the surface of the surface layer of the polyester film substrate is 0.020 pieces / cm ２The following are the laminated biaxially oriented polyester film for release film as described in [1]: [3] The release film as described in [1] or [2], wherein the release layer is formed by curing a composition containing a release agent and a melamine compound. [4] The release film as described in any one of [1] to [3], wherein the weight-average degree of polymerization of the melamine compound is 2.0 or less. [5] The release film as described in any one of [1] to [4], wherein the content of the melamine compound is 80% by mass or more relative to the solid content of the release layer forming composition. [6] The release film as described in any one of [1] to [5], wherein the release agent is a polyorganosiloxane having a functional group that can react with a melamine compound. [7] The release film as described in any one of [1] to [6], wherein the release agent is a polyorganosiloxane containing a carboxyl group. [8] A laminated biaxially oriented polyester film for release film according to any one of [1] to [7], wherein the intrinsic viscosity of the surface layer is 0.55 to 0.62 dl / g. [9] The number of antimony element-containing protrusions present on the surface of the surface layer is 0.010 per cm. ２ A laminated biaxially oriented polyester film for release film according to any one of [1] to [8] below.

[10] A release film according to any one of [1] to [9], wherein the release film is for manufacturing ceramic green sheets or resin sheets.

[0015] According to the present invention, a release film can be provided that has a reduced number of protrusions on the surface layer and high longitudinal breaking strength. Furthermore, the release film of the present invention can prevent pinholes and localized thickness variations even when, for example, a ceramic green sheet or a resin sheet is made into a thin film.

[0016] In this specification, the phrase "contains" is used to include the phrases "essentially consist of" and "consist of".

[0017] In the numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in a given step may be arbitrarily combined with the upper or lower limit of a numerical range in that paragraph or in another step. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with a value shown in the example or a value that can be uniquely derived from the example.

[0018] In this specification, numbers enclosed in "~" represent a numerical range that includes the numbers before and after "~" as the lower and upper limits, respectively. For example, "1 to 10 mass%" is synonymous with "1 mass% or more, and 10 mass% or less."

[0019] In this specification, with respect to numerical ranges, "~" means greater than or equal to the leftmost number and less than or equal to the rightmost number. For example, "0.5~10 mass%" and "0.5 mass%~10 mass%" both mean "0.5 mass% or more and 10 mass% or less." Also, with respect to numerical ranges, "greater than or equal to" means "the same as or greater than," and "less than or equal to" means "the same as or less than."

[0020] A release film may consist of a polyester film that serves 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 release films.

[0021] (Laminated biaxially oriented polyester film for release film) The base film of the present invention includes at least a surface layer (hereinafter also referred to as layer A) and a smooth-slip layer (hereinafter also referred to as layer B). The surface layer is one outermost layer of the base film, and the smooth-slip layer is the other outermost layer. In addition to the surface layer and the smooth-slip layer, the base film preferably includes an intermediate layer (hereinafter also referred to as layer C) between the surface layer and the smooth-slip layer. Therefore, the layer configuration in the thickness direction of the base film can be A / B or A / C / B. The release layer is formed on the surface layer to constitute the release film. Therefore, the layer configuration 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 less expensive than the surface layer and the smooth-slip layer, including the intermediate layer can reduce the thickness of the surface layer and the smooth-slip layer, making the base film less expensive.

[0022] The thickness ratio of the surface layer can be 30% to 50% of the total thickness when an intermediate layer is provided and the layer configuration in the thickness direction is A / C / B, and can be 50% to 90% of the total thickness when an intermediate layer is not provided and the layer configuration in the thickness direction is A / B. The thickness of the surface layer can be 3.6 μm to 50 μm, preferably 4.5 μm to 40 μm. The thickness ratio of the smooth layer can be 10% to 30% of the total thickness when an intermediate layer is provided and the layer configuration in the thickness direction is A / C / B, and can be 10% to 50% of the total thickness when an intermediate layer is not provided and the layer configuration in the thickness direction is A / B. The thickness of the smooth layer can be 3.6 μm to 50 μm, preferably 4.5 μm to 40 μm. The thickness ratio of the intermediate layer can be 20% to 60% of the total thickness. The thickness of the intermediate layer can be 3.6 μm to 50 μm, preferably 4.5 μm to 40 μm. The thickness of the base film can be 12 μm to 100 μm, preferably 15 μm to 80 μm. The film thickness is not particularly limited and can be measured by known methods, but it can be observed and measured using an optical interference film thickness gauge or by observing the cross-section with a scanning electron microscope or transmission electron microscope.

[0023] The base film of the present invention is a laminated biaxially stretched polyester film for a release film, and has a surface layer for laminating a release layer and a lubricating 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. It is preferable that the intrinsic viscosity of the surface layer is 0.55 dl / g or more. It is preferable that the antimony element content of the surface layer is 120 ppm or less.

[0024] The antimony compound contained in the surface layer can be used alone or in combination of two or more. The antimony compound can be an antimony salt of an aliphatic carboxylic acid. The antimony salt of an aliphatic carboxylic acid can be antimony trioxide, antimony pentoxide, antimony acetate, etc., and antimony trioxide is preferable from the viewpoints of polycondensation reactivity, the color tone of the resulting polymer, and easy availability at low cost.

[0025] The content of antimony atoms (antimony compounds) in the surface layer can be an amount such that the antimony atom (element) content in the surface layer is 120 ppm or less. The content of the antimony element is preferably 110 ppm or less, more preferably 90 ppm or less. The content of the antimony element in the surface layer can be specified by an ICP emission analyzer. Specifically, it can be specified by the method described in the examples.

[0026] The alkaline earth metal compound contained in the surface layer can be used alone or in combination of two or more. The alkaline earth metal compound is preferably a magnesium compound. The magnesium compound can be a saturated aliphatic carboxylate, an unsaturated aliphatic carboxylate, an aromatic carboxylate, a halogen-containing carboxylate, a hydroxycarboxylate, a sulfate, a nitrate, a phosphate, a phosphonate, a hydrogen phosphate, a hydrogen sulfide, a sulfite, a thiosulfate, a hydrochloride, a hydrobromide, a chlorate, a bromate of magnesium metal, an organic sulfonate, an organic sulfate, a chelate compound, and an oxide. From the viewpoints of ease of handling and easy availability, etc., a saturated aliphatic carboxylate of magnesium metal is preferable, and magnesium acetate is more preferable.

[0027] The content of the alkaline earth metal compound in the surface layer can be an amount such that the content of the alkaline earth metal element in the surface layer is 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., and an amount of 5 to 100 ppm is preferable, an amount of 5 to 80 ppm is more preferable, and an amount of 5 to 60 ppm is even more preferable. The content of the alkaline earth metal element in the surface layer can be determined by an ICP emission spectrometer. Specifically, it can be determined by the method described in the examples.

[0028] The phosphorus compounds contained in the surface layer can be used singly or in combination of two or more. Examples of the phosphorus compounds include phosphoric acid, phosphorous acid, phosphonic acid, and their derivatives. 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 preferable, and trimethyl phosphate is more preferable.

[0029] The content of the phosphorus compound in the surface layer can be an amount such that the content of the phosphorus element in the surface layer is 50 ppm or less, 40 ppm or less, 30 ppm or less, etc., and an amount of 1 to 50 ppm is preferable, an amount of 1 to 40 ppm is more preferable, and an amount of 1 to 30 ppm is even more preferable.

[0030] The number of protrusions containing antimony element present on the surface of the surface layer is 0.020 pieces / cm ２ or less, 0.015 pieces / cm ２ or less, 0.012 pieces / cm ２ or less, 0.001 to 0.020 pieces / cm ２ 0.001 to 0.015 pieces / cm ２ 0.001 to 0.012 pieces / cm ２ 0.003 to 0.020 pieces / cm ２, 0.003~0.015 pieces / cm ２ , 0.003~0.012 pieces / cm ２ This can range from 0.005 to 0.020 particles / cm². ２ Preferably, 0.005 to 0.015 pieces / cm ２ More preferably, 0.005 to 0.012 pieces / cm ２ This is even more preferable. The number of protrusions containing antimony elements is determined by observing the surface of the surface layer with a scanning white-light interference microscope (magnification 10x), processing the obtained microscope image with the surface analysis software VS-Viewer Version 10.0.3.0 built into the microscope, and measuring the number of protrusions with a height of 0.1 μm or more. Elemental analysis is then performed on the areas where protrusions with a height of 0.1 μm or more were measured using a digital microscope equipped with a laser analysis function, and the number of protrusions with a height of 0.1 μm or more in which antimony elements were detected is measured. The number of measured protrusions is then measured over an observation area (210 mm × 297 mm: area approximately 623.7 cm²). ２ It can be obtained by dividing by ). Specifically, it can be identified by the method described in the examples.

[0031] The antimony content in the surface layer may be 120 ppm or less. Preferably, the antimony content is 110 ppm or less, and more preferably 90 ppm or less. The antimony content in the surface layer can be determined by an ICP emission spectrometer. Specifically, it can be determined by the method described in the examples. A preferred antimony content is 5 ppm or more. If it is lower, polymerization will not proceed, and the release film will not perform as a substrate.

[0032] The alkaline earth metal element content in the surface layer can 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 more preferred, and 5 to 60 ppm even more preferred. Alkaline earth metal elements may form foreign matter in the surface layer. The alkaline earth metal element content in the surface layer can be determined by an ICP emission spectrometer. Specifically, it can be determined by the method described in the examples.

[0033] The phosphorus content in the surface layer can be 50 ppm or less, 40 ppm or less, 30 ppm or less, etc., with 1 to 50 ppm being preferred, 1 to 40 ppm more preferred, and 1 to 30 ppm even more preferred. The phosphorus content in the surface layer can be determined by an ICP emission spectrometer. Specifically, it can be determined by the method described in the examples.

[0034] A sample (10 g) obtained by scraping the surface layer was dissolved in a p-chlorophenol / tetrachloroethane mixture (80 ml), and the resulting solution was filtered under reduced pressure using a membrane filter. The filtered filter was then dried, and the number of particles on the resulting dried filter was measured per 1 mm of the membrane filter. ２ The number of particles per unit may be 400 or less. Hereinafter, the dissolving solution will also be simply referred to as the "dissolving solution," and the drying filter as the "drying filter." The number of particles on the drying filter is as follows: 1 mm of membrane filter ２ Preferably, the number of particles per sheet is 350 or less, more preferably 300 or less, and even more preferably 200 or less. Here, the p-chlorophenol / tetrachloroethane mixture consists only of p-chlorophenol and tetrachloroethane, with a mass ratio of p-chlorophenol 3: tetrachloroethane 1. 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 has a thickness of 90 μm. The membrane filter may be, for example, T050A047A manufactured by ADVANTEC. In this 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 constituting the surface layer. The number of particles on the dry filter can be determined by observing the dry filter at a magnification of 1,000x using a scanning electron microscope (SEM). Specifically, it can be determined by the method described in the examples.

[0035] The antimony element content of the particles filtered on the dry filter may be 10 mg or less per 1 kg of surface layer. Preferably, the antimony element content is 6 mg or less per 1 kg of surface layer, more preferably 5 mg or less, and even more preferably 4 mg or less. 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, 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 amount of Sb element per 10 g of surface layer using fluorescent X-rays on the particles on the dry filter, and then converting this to the amount per 1 kg of polyester film. Specifically, it can be determined by the method described in the examples.

[0036] In the particles filtered on the dry filter, the proportion of particles containing antimony may be 30% or less. Preferably, the proportion of particles containing antimony on the dry filter is 28% or less, more preferably 25% or less, and even more preferably 20% or less. 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 is detected (Sb-containing particles), and calculating the proportion (%) of Sb-containing particles by dividing the number of particles in which Sb is detected by the total number of particles on the dry filter. Specifically, it can be determined by the method described in the examples.

[0037] The number of particles filtered out on the dry filter is per 1 mm of filter. ２ The number of particles per filter may be 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 200 or less. The number of particles filtered out on the dry filter can be determined by observing the dry filter at a magnification of 1,000x using a scanning electron microscope (SEM) and measuring the number of particles. Specifically, it can be determined by the method described in the examples.

[0038] The intrinsic viscosity of the surface layer and the base film may be 0.55 dl / g or higher, respectively. The intrinsic viscosity can be controlled by adjusting the polymerization conditions of the polyester resin constituting the surface layer (polymerization time, addition of solid-phase polymerization, etc.). The intrinsic viscosity may be 0.56 dl / g or higher, 0.57 dl / g or higher, 0.58 dl / g or higher, 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. When the intrinsic viscosity is within the above range, it is advantageous in that the breaking strength of the base film is increased and the thermal shrinkage rate of the base film is reduced. The intrinsic viscosity can be determined in accordance with JIS K 7367-5. The measurement is performed by using a mixed solvent of phenol (6 parts by mass) and 1,1,2,2-tetrachloroethane (4 parts by mass) on a sample obtained by scraping the surface layer or on a substrate film, at a temperature of 30°C. Specifically, it can be determined by the method described in the examples.

[0039] The longitudinal thermal shrinkage rate of the base film under the heat conditions of 150°C for 30 minutes may be 1.4% or less. The longitudinal thermal shrinkage rate can be controlled by adjusting the intrinsic viscosity of the polyester resin constituting the surface layer. The longitudinal thermal shrinkage rate is preferably 1.0% or less, and more preferably 0.9% or less. When the longitudinal thermal shrinkage rate is within the above range, excellent dimensional stability at high temperatures is achieved. In the manufacture of internal electrodes for capacitors, a conductive paste is applied to a release film, dried to form a conductive layer, and the internal electrodes are printed on the conductive layer. Therefore, a small longitudinal thermal shrinkage rate of the base film at high temperatures contributes to suppressing thermal shrinkage of the release film, etc., making it easier to print and form the internal electrodes with high precision. The longitudinal thermal shrinkage rate can be determined by heat-treating a base film with a width of 10 mm and a longitudinal length of 220 mm in a hot air oven at 150°C for 30 minutes and comparing the longitudinal dimensions before and after heat treatment. Specifically, it can be determined by the method described in the examples.

[0040] The longitudinal breaking strength of the base film can be 170 MPa or more, 180 MPa or more, or 190 MPa or more. A breaking strength of 170 to 300 MPa is preferred, 180 to 280 MPa is more preferred, and 190 to 260 MPa is even more preferred. Having a longitudinal breaking strength within this range is advantageous because it reduces the likelihood of defects such as cracking, tearing, folding, or ripping 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.

[0041] The surface layer may be a film made of polyester resin (preferably polyethylene terephthalate). Therefore, the surface layer may contain polyester resin (preferably polyethylene terephthalate). The polyester resin content 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.

[0042] Polyester resin, the raw material for the surface layer, can be produced by a direct reaction between dicarboxylic acid and glycol, a transesterification method in which alkyl esters of dicarboxylic acid (e.g., dialkyl esters (e.g., dimethyl ester, diethyl ester, dibutyl ester)) are transesterified with glycol followed by polycondensation, or by polycondensation of diglycol esters of dicarboxylic acid. For example, polyethylene terephthalate can be produced by an esterification or transesterification reaction of terephthalic acid or dimethyl terephthalate with ethylene glycol to produce an oligomer mixture such as bis(2-hydroxyethyl) terephthalate, which can then be produced by melt polymerization using a catalyst under high temperature and vacuum. In addition, the molten polymer can be solid-phase polymerized at a temperature below its melting point. By performing solid-phase polymerization after melt polymerization, the generation of foreign matter with a major diameter of 1 μm or more and antimony-based foreign matter (particles containing antimony elements) can be suppressed while increasing the intrinsic viscosity and lowering the acid value.

[0043] Dicarboxylic acids can be used individually or in combination of two or more. Dicarboxylic acids may be aromatic dicarboxylic acids, aliphatic dicarboxylic acids, etc., with aromatic dicarboxylic acids being preferred.

[0044] Aromatic carboxylic acids can 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'-biphenylsulfondicarboxylic acid, 4,4'-biphenyletherdicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, pamoic acid, anthracenedicarboxylic acid, etc. Terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid are preferred, with terephthalic acid being more preferred.

[0045] Aliphatic dicarboxylic acids can be saturated aliphatic dicarboxylic acids 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, and dimer acid; or unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid.

[0046] Diols can be used individually or in combination of two or more. Diols may be aliphatic glycols, aromatic glycols, etc., with aliphatic glycols being preferred.

[0047] 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. These may be alkylene glycols such as polyethylene glycol, polytrimethylene glycol, polytetramethylene glycol, etc.; aliphatic glycols such as polyethylene glycol, polytrimethylene glycol, polytetramethylene glycol, etc.; 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.

[0048] The surface layer may be 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 surface layer may be polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, or polyethylene-2,6-naphthalate, with polyethylene terephthalate being preferred.

[0049] The polyester resin constituting the surface layer is preferably a polyester resin in which the main dicarboxylic acid component is terephthalic acid, or a polyester resin in which the main diol component is ethylene glycol, and more preferably a polyester resin (polyethylene terephthalate) in which the main dicarboxylic acid component is terephthalic acid and the main diol component is ethylene glycol.

[0050] Here, the main dicarboxylic acid component means that, when the total dicarboxylic acid component in the polyester resin is set to 100 mol%, the dicarboxylic acid or its ester component is 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 100 mol%.

[0051] Furthermore, the term "main diol component" means that, when the total diol component in the polyester resin is considered to be 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%.

[0052] Polymerization catalysts may be used in melt polymerization for the production of polyester resins. Polymerization catalysts may be used individually or in combination of two or more types. Antimony compounds are preferred as polymerization catalysts. Antimony compounds may be used individually or in combination of two or more types. Antimony compounds may be antimony salts of aliphatic carboxylic acids. Antimony salts of aliphatic carboxylic acids may be antimony trioxide, antimony pentoxide, or antimony acetate, and antimony trioxide is preferred in terms of polycondensation reactivity, the color of the resulting polymer, and its low cost. 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 as long as they do not cause problems with the surface layer properties.

[0053] When manufacturing polyester resins, it is preferable to add alkaline earth metals. Alkaline earth metal compounds can be used individually or in combination of two or more. Magnesium compounds are preferred among the alkaline earth metal compounds. Magnesium compounds can be saturated aliphatic carboxylates, unsaturated aliphatic carboxylates, aromatic carboxylates, halogen-containing carboxylates, hydroxycarboxylates, sulfates, nitric acid, phosphoric acid, phosphonic acid, hydrogen phosphate, hydrogen sulfide, sulfite, thiosulfate, hydrochloric acid, hydrobromic acid, chloric acid, bromate, inorganic salts selected from these, organic sulfonates, organic sulfates, chelate compounds, and oxides of magnesium metal. From the viewpoint of ease of handling and availability, saturated aliphatic carboxylates of magnesium metal are preferred, and magnesium acetate is more preferred.

[0054] When manufacturing polyester resins, it is preferable to add a phosphorus compound as a heat stabilizer. The phosphorus compound may be used alone or in combination of two or more. Examples of phosphorus compounds include phosphoric acid, phosphorous acid, phosphonic acid, and their derivatives. Specific examples include phosphoric acid, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphorous acid, trimethyl phosphorous acid, tributyl phosphorous acid, methylphosphonic acid, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, and diphenyl phenylphosphonate. Among these, trimethyl phosphate, diethyl ethylphosphonate, and / or phosphoric acid are preferred, with trimethyl phosphate being more preferred.

[0055] When manufacturing polyester resin, various compounds and additives may be added, as long as they do not cause problems with the properties of the resulting surface layer.

[0056] An example of the manufacturing process for the polyester resin constituting the surface layer is as follows. Note that the polyester resin described below is polyethylene terephthalate. The present invention may be a method for manufacturing a biaxially oriented polyester film for the surface layer constituting a release film, comprising the following steps 1 to 3.

[0057] [Step 1] A step to obtain a polyester resin by melt polymerization using terephthalic acid as the main component of the dicarboxylic acid and ethylene glycol as the main component of the diol, with an antimony compound as the main polymerization catalyst. [Step 2] Optionally, a step to obtain a polyester resin by solid-phase polymerization of the polyester resin obtained in Step 1 at 197 to 225°C for 5 to 10 hours. [Step 3] A step to obtain a biaxially oriented polyester film for the surface layer constituting the release film by stretching the polyester resin obtained in Step 1 or 2.

[0058] Melt polymerization may be carried out by a batch polymerization method or a continuous polymerization method. In either method, the esterification reaction or transesterification reaction may be carried out in one step, but it is preferable to carry it out in multiple steps. In the melt polymerization reaction, the number and size of reactors and the manufacturing conditions of each step can be selected as appropriate without limitation, and it may be carried out in one step or in multiple steps, preferably in 2 to 5 steps, more preferably in 3 to 4 steps, and even more preferably in 3 steps. The melt polymerization reaction is preferably carried out in a continuous reactor. A continuous reactor is a method in which the reaction vessel for the esterification reaction or transesterification reaction and the melt polymerization reaction vessel are connected by piping, and raw materials are continuously fed into each reaction vessel, transferred to the melt polymerization reaction vessel via piping, and resin is withdrawn from the melt polymerization reaction vessel without allowing each reaction vessel to be emptied.

[0059] The process for the continuous polymerization method is as follows:

[0060] 1) Slurry preparation step: The dicarboxylic acid component and the diol component are introduced into a slurry preparation tank to prepare the slurry. The proportion of these components in the slurry is not particularly limited as long as the slurry has sufficient fluidity to be transported to the esterification reaction tank. Furthermore, from an economic standpoint, it is preferable to reuse the diol component recovered in the polycondensation step as a slurry raw material. In this invention, recycled raw materials such as dicarboxylic acid components and diol components obtained by chemical decomposition recovery may also be used.

[0061] 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 diols are condensed on both terminal carboxyl groups of the dicarboxylic acid component. The esterification reaction is preferably carried out while removing the water produced by the reaction from the system using a distillation column. The number and size of reaction vessels in the esterification reaction step are not limited and can be selected as appropriate. In addition, the manufacturing conditions for each step can be appropriately selected depending on the type and amount of polycondensation catalyst and additives for improving electrostatic adhesion, the number and size of reaction vessels, etc. For example, if there are three esterification reaction vessels, the temperature of the first esterification reaction vessel may be 240 to 270°C, the pressure may be 100 to 160 kPa in absolute pressure, and the average residence time may be 2 to 5 hours. When solid-phase polymerization is not used, the average residence time is preferably 3.5 to 5 hours, and 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 0 to 100 kPa in absolute pressure, and the average residence time 0.1 to 2.5 hours. When solid-phase polymerization is not used, the average residence time for 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 for the third esterification reaction is preferably 1.0 to 2.5 hours, more preferably 1.1 to 2.5 hours. Ultimately, it is desirable that the esterification reaction rate reaches 60% or more, preferably 70% or more. Furthermore, as the esterification reaction vessel, a multi-stage reaction within a single vessel may be used, with a weir or the like installed inside.

[0062] In the esterification process, it is preferable to supply additional diol components from the second esterification reactor onward. If the entire amount of diol components is supplied during slurry preparation, there is a problem that the composition of diol components in the polyester resin may fluctuate or the esterification reaction rate may decrease when continuous production is carried out over a long period of time. By supplying additional diol components from the second esterification reactor onward, this problem can be suppressed.

[0063] In the esterification step, phosphorus compounds, alkali metal compounds, alkaline earth metal compounds, etc., may be added. The timing of the addition can be anytime between before the esterification reaction and the start of the polycondensation reaction, but in the continuous polymerization method, it is preferable to add them in the third esterification reaction vessel or later.

[0064] When producing polyester resin by batch polymerization or continuous polymerization, methods for adding antimony compounds include powder, ethylene glycol slurry, or ethylene glycol solution, but adding it as an ethylene glycol solution is preferred. The timing of addition may be either before the esterification and transesterification reactions, or between the completion of the transesterification and esterification reactions and the start of the polycondensation reaction.

[0065] 3) Polycondensation reaction step The oligomer compound that has undergone the esterification reaction is subsequently transferred to a polycondensation reaction vessel and subjected to a polycondensation reaction. The number and size of the reaction vessels in the polycondensation reaction step are not limited and can be selected as appropriate. Furthermore, the manufacturing conditions for each step can be selected as appropriate depending on the type and amount of the polycondensation catalyst and additives, the number and size of the reaction vessels, etc. For example, if there are three polycondensation reaction vessels, the temperature of the first polycondensation reaction vessel may be 260 to 290°C, the pressure may be 2 to 8 kPa, and the average residence time may be 0.1 to 1 hour. When solid-phase polymerization is not used, the average residence time of the first polycondensation is preferably 0.8 to 1 hour, and more preferably 0.9 to 1 hour. The temperature of the second polycondensation reaction vessel may be 270 to 290°C, the pressure may be 0.5 to 1.5 kPa, and the average residence time may be 0.1 to 2 hours. When solid-phase polymerization is not used, the average residence time for the second polycondensation is preferably 1.0 to 2 hours, and more preferably 1.1 to 2 hours. The temperature of the third polycondensation reaction vessel may be 270 to 290°C, the pressure 0.01 to 0.5 kPa, and the average residence time 0.1 to 2 hours. When solid-phase polymerization is not used, the average residence time for the third polycondensation is preferably 1.0 to 2 hours, and 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 is smoothly distributed. Since diol components are distilled off in the polycondensation reaction step, it is preferable to recover, purify, and reuse them. This recovery and purification can be carried out in a distillation column, similar to the esterification reaction step.

[0066] The intrinsic viscosity of the polyester resin produced by melt polymerization is preferably 0.52 to 0.59 dl / g, and more preferably 0.52 to 0.55 dl / g. Having the intrinsic viscosity of the polyester resin within this range is advantageous because it suppresses the formation of foreign matter.

[0067] Further solid-phase polymerization of the polyester resin obtained by melt polymerization is preferable because it reduces the number of antimony element-containing protrusions and increases the longitudinal tensile strength of the base film.

[0068] Solid-phase polymerization can be carried out on polyester resin in the form of powder or granules. The term "powder or granules" refers to chips, pellets, flakes, or powder, but pellets are preferred.

[0069] Solid-phase polymerization can be carried out by heating a granular polyester resin at a temperature below the melting point of the polyester resin under the flow of an inert gas or under reduced pressure. It is preferable to carry out the solid-phase polymerization under reduced pressure. The solid-phase polymerization process may be carried out in one step or in multiple steps. It is preferable that the granular polyester resin supplied to the solid-phase polymerization process is first heated to a temperature lower than the temperature at which solid-phase polymerization will be carried out to crystallize it before being supplied to the solid-phase 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 to a temperature of usually 120 to 200°C, preferably 130 to 150°C, for 1 to 4 hours.

[0070] 4) Stretching Process The polyester resin is stretched to form a film. Stretching can improve chemical resistance, heat resistance, mechanical strength, etc. It is preferable to co-extrude a polyester resin for the surface layer, a polyester resin for the smooth layer, and, if the base film has an intermediate layer, a polyester resin for the intermediate layer, to form a two- or three-layer laminated sheet, or to form each polyester resin into a sheet (for example, melt-extrude the polyester resin into a sheet at 250 to 320°C and then solidify it), then laminate these sheets together to form a two- or three-layer laminated sheet, and then stretch these laminated sheets. A base film can be obtained by stretching the laminated sheet. Stretching can be carried out by known methods. For example, a method can be used in which the laminated sheet is sequentially or simultaneously biaxially stretched longitudinally and transversely at 70°C to 140°C, and then heat-treated at 160 to 240°C to obtain a base film. Typically, the stretching ratio can be selected from a range of 1.1 to 10 times in both the longitudinal (longitudinal) and transverse (width) directions. The stretching ratio in the longitudinal direction 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. The stretching ratio in the width direction 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. When the stretching ratio is within the above range, it is advantageous in that the thickness unevenness of the resulting base film is suppressed, and the heat resistance and mechanical strength are excellent. In this invention, the stretching ratio is defined as the actual stretching ratio of the base film. This stretching ratio can be determined by measuring the mass change rate per unit area before and after each stretching process, or by marking the unstretched film with a grid of stretching ratio markers.

[0071] The surface layer may contain particles, but from the viewpoint of reducing surface irregularities, it is preferable that it does not contain particles with an average particle diameter of 1.0 μm or more. Examples of particles include inorganic particles such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, as well as organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. The particles may be used individually or in combination of two or more types. As particles, titanium dioxide, calcium carbonate, and silica are preferred due to their high versatility. The average particle diameter of the particles is preferably 1 nm or more and less than 1.0 μm.

[0072] The base film may have a slip-free layer on the outermost layer opposite the surface layer. The slip-free layer contains lubricant particles and polyester resin. The slip-free layer may be a film made of polyester resin (preferably polyethylene terephthalate). The slip-free layer may contain lubricant particles and polyester resin (preferably polyethylene terephthalate). The content of polyester resin in the slip-free layer may be 70-90% by mass, 80-90% by mass, 70-95% by mass, 80-95% by mass, 90-95% by mass, 70-100% by mass, 80-100% by mass, 90-100% by mass, 95-100% by mass, etc.

[0073] The smooth layer may be a biaxially oriented 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 smooth 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 make it stronger. In this case, known crosslinking agents such as isocyanate resins and melamine resins can be used.

[0074] Examples of lubricant particles contained in the smooth layer include inorganic particles such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, as well as organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. From the viewpoint of the film's slipperiness and ease of air release, at least one particle selected from calcium carbonate particles or silica particles is preferred as the lubricant particle.

[0075] The lower limit of the particle size of the lubricant particles contained in the smooth layer is preferably 5 nm, more preferably 10 nm, and even more preferably 15 nm. A particle size of 5 nm or more is preferable as it satisfies the slipperiness requirements and does not risk causing winding misalignment. The upper limit of the particle size in the smooth layer is preferably 100 nm, more preferably 90 nm, and even more preferably 80 nm. A particle size of 100 nm or less is preferable as it reduces the surface roughness of the smooth layer and does not risk transferring large surface roughness to the release layer. The particle size of the lubricant particles can be 5 to 100 nm, 5 to 90 nm, 5 to 80 nm, 10 to 100 nm, 10 to 90 nm, 10 to 80 nm, 15 to 100 nm, 15 to 90 nm, or 15 to 80 nm.

[0076] The amount of lubricant particles contained in the smoothing layer may be 5,000 to 15,000 ppm, 3,000 to 15,000 ppm, or 500 to 10,000 ppm.

[0077] The smoothing layer may contain surfactants to improve leveling properties during application and to defoam the coating solution. The surfactant can be cationic, anionic, or nonionic, but silicone-based, acetylene glycol-based, or fluorine-based surfactants are preferred. These surfactants should be included in the coating layer in an amount that does not cause abnormalities in the appearance of the coating due to excessive addition.

[0078] The smooth layer can be formed by depositing it on the surface layer in the case of layer configuration A / B, or on the intermediate layer in the case of layer configuration A / C / B, using a known method. Conventional methods such as co-extrusion and lamination can be used as film-forming methods. Alternatively, by using a multilayer coater die, a coating liquid for surface layer formation and a coating liquid for smooth layer formation can be applied to the intermediate layer to form the surface layer and the smooth layer.

[0079] The base film may or may not have an intermediate layer between the surface layer and the smooth-slip layer.

[0080] Polyester resin may be used as the intermediate layer. To reduce the cost of the base film, resin obtained by recycling polyester film (e.g., release film) may be used. When using recycled resin, the proportion of this resin in the polyester resin is preferably 5 to 50% by mass. The intermediate layer may be a biaxially oriented film made of polyester resin (preferably polyethylene terephthalate). The intermediate layer may contain polyester resin (preferably polyethylene terephthalate). The polyester resin content 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, etc.

[0081] The polyester resin constituting the intermediate layer is not particularly limited, and a film made from a polyester resin commonly used as an intermediate layer in release films can be used. Preferably, it is a crystalline linear saturated polyester composed of an aromatic dibasic acid component and a diol component, and for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or copolymers mainly composed of these resin components are more preferable. In particular, a polyester film formed from polyethylene terephthalate is especially preferable. The polyethylene terephthalate preferably has 90 mol% or more, more preferably 95 mol% or more of repeating units of ethylene terephthalate, and may also have small amounts of other dicarboxylic acid components and diol components copolymerized. From a cost standpoint, it is preferable to have one manufactured only from terephthalic acid and ethylene glycol. In addition, known additives, such as antioxidants, light stabilizers, ultraviolet absorbers, and crystallizers, may be added within a range that does not hinder the effect of the base film.

[0082] (Release layer) The release film of the present invention has a surface free energy of 18 to 35 mJ / m² on the surface of the release layer. 2 The release layer thickness is 50 nm to 1500 nm, the average surface roughness (Sa) of the surface of the release layer is 7 nm or less, and the maximum protrusion height is 100 nm or less. The present invention has a release layer on the surface of the polyester film substrate according to this specification, so the generation of protrusions can be suppressed. Furthermore, with the release layer of the present invention, the effects of the polyester film substrate can be enjoyed even when the release layer is laminated. Therefore, the release film of the present invention can also achieve high tensile strength in the longitudinal direction and low stability of thermal shrinkage.

[0083] (Structure of the release layer) The release layer in the present invention is formed by curing a release layer forming composition, which contains a release agent and a melamine compound. For example, the release layer forming composition contains a melamine compound and a polyorganosiloxane having a functional group that can react with the melamine compound. Other components besides the resin and additives can be added as long as they do not impair the effects of the present invention.

[0084] The melamine-based compound used in the release layer of the present invention can be any common compound and is not particularly limited, but it is preferable that it is obtained by condensing melamine and formaldehyde and has one or more triazine rings and one or more methylol groups and / or alkoxymethyl groups in one molecule. Specifically, a compound obtained by dehydrating and condensing a methylolmelamine derivative obtained by condensing melamine and formaldehyde with a lower alcohol such as methyl alcohol, ethyl alcohol, isopropyl alcohol, or butyl alcohol to obtain an ether compound is preferred. Examples of methylolated melamine derivatives include monomethylolmelamine, dimethylolmelamine, trimethylolmelamine, tetramethylolmelamine, pentamethylolmelamine, and hexamethylolmelamine. One type or two or more types may be used.

[0085] In the present invention, the release layer preferably has a high crosslink density and high modulus of elasticity in order to suppress deformation of the release layer during peeling and to make the peeling force low and uniform. For this reason, it is preferable to use hexamethylolmelamine or hexalokkoxymethylmelamine, which have many crosslinking points in one molecule, but hexalokkoxymethylmelamine is more preferable due to its superior reactivity, and in particular, hexamethoxymethylmelamine is preferred. In this case, hexamethylolmelamine is defined as the following formula (a) in which X is a methylol group (-CH ２ It is (-OH). Hexaalkoxymethylmelamine is obtained by dehydration condensation reaction of a methylolmelamine derivative with alcohol, and X is (-CH ２ It is a compound where -OR (where R is an alkyl group having 1 to 4 carbon atoms). Hexamethoxymethylmelamine is a compound where X is (-CH ２ -OMe) is the case.

[0086]

[0087] In (a) above, X may be the same or different. Similarly, R may be the same or different. Also, X may be (-H).

[0088] In the melamine-based compound used in the release layer of the present invention, the weight-average molecular weight is preferably 250 or more and 1000 or less. More preferably, the weight-average molecular weight is 250 or more and 900 or less, and even more preferably 300 or more and 800 or less. A weight-average molecular weight of 1000 or less is preferable because the crosslinking reaction proceeds easily, a film with a higher crosslinking density can be formed, and the peeling force can be reduced. A weight-average molecular weight of 250 or more is preferable because the crosslinking density does not become excessively high and curling does not deteriorate. The weight-average molecular weight in this specification is the value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0089] The fact that the weight-average molecular weight of the melamine compound is 250 to 1000 means that the melamine compound used in this invention contains a large amount of mononuclear material. Mononuclear material has more crosslinking sites and better reactivity than polynuclear material formed by the condensation of two or more melamine derivatives, so it can be used to create a release layer with a high crosslinking density and excellent release properties. The higher the mononuclear content, the better, and it is most preferable to use a melamine compound consisting only of mononuclear material.

[0090] The weight-average molecular weight can also be expressed as the weight-average degree of polymerization. The weight-average degree of polymerization of the melamine compound used is preferably 2.0 or less, more preferably 1.5 or less, and the smaller the value, the more suitable it is for use. A weight-average degree of polymerization of 2.0 or less is preferable because it increases the mononuclear content of the melamine compound, resulting in a release layer with excellent reactivity and peelability. In this specification, the weight-average degree of polymerization is a value calculated based on the weight-average molecular weight obtained by gel permeation chromatography on a standard polystyrene basis. A weight-average degree of polymerization of 1.1 or more is preferable.

[0091] Melamine compounds, in their synthesis process, involve the imino group (-NH ２Some may contain (-) or polynuclear compounds. Even if these melamine derivatives are mixed, as long as the weight-average molecular weight (i.e., weight-average degree of polymerization) of the melamine compounds is within the above range, they exhibit excellent reactivity and can be used suitably.

[0092] In the present invention, the release layer preferably contains 80% to 99.9% by mass of a melamine compound relative to the solid content of the release layer forming composition, more preferably 90% to 99.9% by mass, and even more preferably 95% to 99.9% by mass. By including 80% or more by mass of a melamine compound, the release layer can obtain a high crosslinking density through self-crosslinking of the melamine compound, thereby suppressing deformation of the release layer during peeling. In this case, the solid content of the release layer forming composition can be considered to be substantially the sum of the solid content of the melamine compound and the release agent, since a considerable portion of the solvent and acid catalyst evaporates during the drying process. For example, the total solid content of the release layer can be calculated by taking the solid content of the melamine compound and the release agent contained in the release layer forming composition as 100% by mass. In another embodiment, if the release layer forming composition contains a catalyst, the total solid content of the release layer can be calculated by taking the solid content of the melamine compound, release agent, and catalyst contained in the release layer forming composition as 100% by mass.

[0093] In the present invention, it is preferable to add an acid catalyst to the release layer to promote the crosslinking reaction of the melamine compound, and it is preferable to add the acid catalyst to the release layer forming composition, apply it, and cure it. It is preferable to use a sulfonic acid-based catalyst as the acid catalyst.

[0094] As sulfonic acid catalysts, for example, p-toluenesulfonic acid, xylenesulfonic acid, cumenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and trifluoromethanesulfonic acid can be suitably used, but from the viewpoint of reactivity, p-toluenesulfonic acid can be particularly suitably used.

[0095] The sulfonic acid catalyst used in the present invention can also be a commercially available one. Examples of commercially available products include Dryer® 900 (p-toluenesulfonic acid, manufactured by Hitachi Chemical Co., Ltd.), NACURE® DNNDSA series (dinonylnaphthalene disulfonic acid, manufactured by Kusumoto Chemical Co., Ltd.), NACURE® DNNSA series (dinonylnaphthalene (mono)sulfonic acid, manufactured by Kusumoto Chemical Co., Ltd.), NACURE® DDBSA series (dodecylbenzenesulfonic acid, manufactured by Kusumoto Chemical Co., Ltd.), and NACURE® p-TSA series (p-toluenesulfonic acid, manufactured by Kusumoto Chemical Co., Ltd.).

[0096] Sulfonic acid-based catalysts have higher acidity and superior reactivity compared to other acid catalysts such as carboxylic acid-based catalysts, allowing for the processing of the release layer at lower temperatures. This is preferable because it suppresses the decrease in film flatness and deterioration of the winding appearance caused by heat during processing.

[0097] The amount of acid catalyst added is preferably 0.1 to 10% by mass relative to the melamine-based compound contained in the release layer. More preferably, it is 0.5 to 8% by mass. Even more preferably, it is 0.5 to 7% by mass. An amount of 0.1% by mass or more is preferable because it facilitates the curing reaction. On the other hand, an amount of 10% by mass or less is preferable because there is no risk of the acid catalyst migrating to the ceramic green sheet being molded, thus avoiding any adverse effects.

[0098] In the present invention, a release agent (an additive that improves the release properties of the release layer) used in the release layer can be a release agent having a functional group that can react with a melamine compound. From the viewpoint of achieving both release properties and suppression of migration, it is preferable to use a polyorganosiloxane containing a reactive group as the release agent. The reactive group is not particularly limited as long as it can react with a melamine compound, and carboxyl groups and hydroxyl groups can be used. Among polyorganosiloxane structures, a polyorganosiloxane containing a carboxyl group having a polydimethylsiloxane structure (abbreviated as PDMS) can be suitably used.

[0099] The presence of carboxyl groups in the polyorganosiloxane, which is used as a release agent, prevents the release agent from strongly interacting with melamine compounds during the drying process, allowing it to easily orient itself on the surface of the release layer and resulting in good release properties. Therefore, using a polyorganosiloxane containing carboxyl groups is preferable because it allows for satisfactory release properties even with a small amount of release agent added. Furthermore, the presence of carboxyl groups in the polyorganosiloxane, which is used as a release agent, results in weak interactions with melamine compounds, making migration to the ceramic green sheet less likely.

[0100] The carboxyl group may be introduced at one end of the polyorganosiloxane, at both ends, or in the side chains, but it is preferable to introduce it at one end because it has better exfoliation properties. Also, there may be one or more positions where the group is introduced.

[0101] Regarding carboxyl-modified polyorganosiloxanes, the carboxyl group may be directly bonded to the silicon atom of the polyorganosiloxane, or it may be bonded to the polyorganosiloxane via an alkyl or aryl group. However, polyorganosiloxanes to which the carboxyl group is bonded via repeating organic groups such as polyethers, polyesters, and polyurethanes are not particularly preferred.

[0102] The functional group introduced into the polyorganosiloxane, which is used as a mold release agent, may contain other functional groups besides carboxyl groups within a single molecule, but it is preferable to have only carboxyl groups. Including functional groups other than carboxyl groups is undesirable because it may increase intermolecular interactions with melamine-based compounds excessively, making it difficult for the compound to orient itself to the surface of the mold release layer.

[0103] The polyorganosiloxane used in the present invention preferably has a molecular weight of 40,000 or less. More preferably, it has a molecular weight of 30,000 or less. A molecular weight of 40,000 or less is preferable because the polyorganosiloxane containing carboxyl groups tends to segregate on the surface of the release layer, resulting in good release properties.

[0104] As mentioned above, the polyorganosiloxane containing a carboxyl group is more preferably a polydimethylsiloxane containing a carboxyl group. Examples of polydimethylsiloxanes containing a carboxyl group include X22-3701E (side-chain carboxyl-modified polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd.), X22-3710 (one-end carboxyl-modified polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd.), X22-162C (both-end carboxyl-modified polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd.), BY16-750 (both-end carboxyl-modified polydimethylsiloxane, manufactured by Toray Dow Corning Co., Ltd.), BY16-880 (side-chain carboxyl-modified polydimethylsiloxane, manufactured by Toray Dow Corning Co., Ltd.), and Magnasoft 800L (both-end carboxyl-modified polydimethylsiloxane, manufactured by Momentive Co., Ltd.).

[0105] The polydimethylsiloxane containing carboxyl groups in the present invention may be an acrylic resin in which polydimethylsiloxane is introduced as a side chain to an acrylic main chain containing carboxyl groups. Examples of acrylic resins in which polydimethylsiloxane is introduced as a side chain to an acrylic main chain containing carboxyl groups include Cymac® US-350, US-352, and US-380 (all manufactured by Toagosei Co., Ltd.). Alternatively, the acrylic resin may be one in which polydimethylsiloxane is introduced as a side chain to an acrylic main chain containing both carboxyl and hydroxyl groups in one molecule. Examples of acrylic resins in which polydimethylsiloxane is introduced as a side chain to an acrylic main chain containing both carboxyl and hydroxyl groups in one molecule include Cymac® US-450 and US-480 (all manufactured by Toagosei Co., Ltd.).

[0106] In the present invention, the release layer preferably contains a release agent in an amount of 0.1% by mass or more and 20% by mass or less relative to the solid content of the release layer forming composition. More preferably, it is 0.1% by mass or more and 10% by mass or less, and even more preferably, 0.1% by mass or more and 5% by mass or less. An amount of 0.1% by mass or more is preferable because it improves release properties and improves the peelability of the ceramic green sheet. On the other hand, an amount of 20% by mass or less is preferable because it prevents the overall elastic modulus of the release layer from decreasing too much, and suppresses deformation of the release layer and increased peeling force when peeling the ceramic green sheet. Furthermore, an amount of 20% by mass or less is also preferable because it prevents the amount of release agent migration from becoming too high. In this case, the solid content of the release layer forming composition can be considered to be substantially the sum of the solid content of the melamine compound and the release agent, since a considerable portion of the solvent and acid catalyst evaporates during the drying process.

[0107] The release layer in the present invention may contain particles with a particle size of 1 μm or less, but from the viewpoint of pinhole generation, it is preferable not to contain particles or other materials that form protrusions.

[0108] In the release layer of the present invention, additives such as adhesion enhancers and antistatic agents may be added, as long as they do not hinder the effects of the present invention. Furthermore, in order to improve adhesion to the substrate, it is also preferable to pre-treat the surface of the polyester film with an anchor coat, corona treatment, plasma treatment, atmospheric pressure plasma treatment, etc., before applying the release coating layer.

[0109] (Characteristics of the release layer) In the present invention, the thickness of the release layer is 50 nm to 1500 nm. Preferably, it is 100 nm to 1500 nm, and 100 nm to 1200 nm. When the thickness of the release layer is 50 nm or more, the average surface roughness (Sa) and the maximum protrusion height of the surface of the release layer can be suppressed within the range of the present invention. Furthermore, when it is 1500 nm or less, the curing time can be shortened, the flatness of the release film is maintained, and thickness unevenness of the ceramic green sheet can be suppressed, which is preferable. In the present invention, when the thickness of the release layer exceeds 1500 nm, it can fully exhibit its function as a release layer, but the curing time of the release layer tends to be longer.

[0110] The release layer surface of the release film of the present invention is preferably flat in order to prevent defects from occurring in the ceramic green sheet coated and molded thereon, and preferably the average surface roughness (Sa) of the region is 7 nm or less and the maximum protrusion height (P) is 100 nm or less. Furthermore, it is more preferable that the average surface roughness of the region is 5 nm or less and the maximum protrusion height is 80 nm or less. If the region surface roughness is 7 nm or less and the maximum protrusion height is 100 nm or less, defects such as pinholes will not occur when forming the ceramic green sheet, resulting in a good yield, which is preferable. It can be said that a smaller average surface roughness (Sa) is preferable, but it may be 0.1 nm or more, or 0.3 nm or more. It can also be said that a smaller maximum protrusion height (P) is preferable, but it may be 1 nm or more, or 3 nm or more. By using the polyester film substrate of the present invention, the average surface roughness (Sa) and maximum protrusion height (P) of the release layer can be brought within the range of the present invention. Furthermore, the present invention enables the release film to exhibit high longitudinal breaking strength, allowing for faster winding and unwinding of the film during manufacturing, for example, compared to conventional methods. In addition, because it achieves low thermal shrinkage stability of the release film, it can maintain dimensional stability of the release film even under high-temperature processing conditions during the manufacturing of ceramic green sheets and resin sheets.

[0111] Because the release film of the present invention uses a highly planarized base film, the surface of the release layer can be made smooth even when the thickness of the release layer is thinner than 0.5 μm, and even thinner than 0.2 μm. Therefore, even if the release layer uses a highly reactive melamine-based compound, the occurrence of curling can be suppressed. In addition, the amount of solvent and resin used can be reduced, making it environmentally friendly and enabling the creation of an inexpensive release film for ultra-thin ceramic green sheet molding.

[0112] The surface free energy (γs) of the release layer surface of the release layer film of the present invention is 18 mJ / m ２ 35mJ / m or more ２ Preferably, the following: More preferably, 23 mJ / m ２ 35mJ / m or more ２The following, and more preferably 23 mJ / m ２ 30mJ / m or more ２ The following is the result: 18 mJ / m ２ A concentration of 35 mJ / m is preferable because it makes it less likely for repellency to occur when applying the ceramic slurry, allowing for uniform coating. ２ The following range is preferable as it does not risk reducing the release properties of the ceramic green sheet. By setting it within the above range, it is possible to provide a release film that does not repel during coating and has excellent release properties.

[0113] The release film of the present invention preferably has a peeling force of 0.5 mN / mm or more and 2.5 mN / mm or less when peeling off the ceramic green sheet. More preferably, it has a peeling force of 0.8 mN / mm or more and 2.0 mN / mm or less. A peeling force of 0.5 mN / mm or more is preferable because the peeling force is not too light and there is no risk of the ceramic green sheet lifting up during transport. A peeling force of 2.5 mN / mm or less is preferable because there is no risk of the ceramic green sheet being damaged during peeling.

[0114] The release film of the present invention is preferable if the amount of silicone component transferred to the ceramic green sheet after peeling is small. The amount of silicone component transferred can be evaluated by simulating coating and molding PVB, one of the binder components contained in the ceramic green sheet, onto the release film, and measuring the Si intensity of the release layer before and after peeling using fluorescent X-rays. More specifically, when the Si intensity of the surface of the release layer is taken as Si(before) and the Si intensity of the release surface of the release film after coating and peeling the PVB sheet is taken as Si(after), the value of Si(before) - Si(after) is taken as the amount of transfer. It is preferable that the amount of transfer in this case is 0.10 kcps or less, and more preferably 0.04 kcps or less. When the amount of transfer is 0.10 kcps or less, the occurrence of process defects such as lamination misalignment and poor adhesion is suppressed, and there is no risk of reducing the reliability of the ceramic capacitor, which is preferable.

[0115] The release layer of the present invention may contain a melamine compound and a polyorganosiloxane, and it is preferable that the polyorganosiloxane has a functional group that can react with the melamine compound. The reaction between the polyorganosiloxane and the melamine compound can suppress the amount of silicone component transferred to the resin sheet.

[0116] The release film of the present invention preferably has a curl of 3 mm or less, and more preferably 1 mm or less, after being heated at 80°C for 5 minutes without tension. Of course, it is also preferable that there is no curl at all. A curl of 3 mm or less is preferable because it reduces curl when molding the ceramic green sheet and printing electrodes, thereby improving printing accuracy.

[0117] In the present invention, the method for forming the release layer is not particularly limited. A coating solution containing a dissolved or dispersed release resin is applied to one side of a polyester film substrate, and after removing the solvent by drying, the film is heated and heat-cured. In this case, the drying temperature during solvent drying and heat curing is preferably 100°C or higher and 180°C or lower, more preferably 100°C or higher and 160°C or lower, and most preferably 100°C or higher and 140°C or lower. The heating time is preferably 30 seconds or less, and more preferably 20 seconds or less. When the temperature is 180°C or lower, the flatness of the film is maintained, and there is little risk of causing uneven thickness in the ceramic green sheet, which is preferable. When the temperature is 140°C or lower, the film can be processed without impairing the flatness of the film, and the risk of causing uneven thickness in the ceramic green sheet is further reduced, which is particularly preferable. When the temperature is lower than 100°C, the melamine curing reaction does not proceed sufficiently, and the elastic modulus of the release layer decreases, which is undesirable.

[0118] In the present invention, the surface tension of the coating liquid when applying the release layer is not particularly limited, but is preferably 30 mN / m or less. By setting the surface tension as described above, the wettability after coating is improved, and the surface irregularities of the coating film after drying can be reduced.

[0119] In the present invention, the coating liquid used when applying the release coating layer is not particularly limited, but it is preferable to add a solvent with a boiling point of 90°C or higher. Adding a solvent with a boiling point of 90°C or higher prevents bumping during drying, allows the coating film to level, and improves the smoothness of the coating film surface after drying. The amount of solvent added is preferably about 10 to 80% by mass of the total coating liquid.

[0120] Any known coating method can be applied to the above coating liquid. For example, conventional methods such as roll coating methods including gravure coating and reverse coating, bar coating methods such as wire bar coating, die coating, spray coating, and air knife coating can be used.

[0121] In the present invention, the release layer may contain additives such as adhesion enhancers and antistatic agents, as long as they do not hinder the effects of the present invention, but it is preferable that it does not contain particles. By not containing particles in the release layer, deterioration of the smoothness of the release layer surface and contamination of the resin sheet with particles due to particle detachment can be suppressed. In order to improve adhesion to the substrate, the polyester film surface may be pretreated with an anchor coat, corona treatment, plasma treatment, atmospheric pressure plasma treatment, etc., before applying the release coating layer.

[0122] The release film of the present invention preferably has a release layer that is less prone to static charge. More specifically regarding static charge, in the release film manufacturing process, when the film is wound up after the release layer is applied and stored in a roll, the static charge that increases over time can be a problem. For example, if the amount of static charge on the rolled film is large, minute environmental foreign matter during the slitting process and the ceramic green sheet molding process, as well as film scraps generated during slitting, are more likely to adhere to the film. Since these foreign matter adhering to the film may be mixed into the ceramic green sheet, potentially leading to defects, it is preferable that the release film has a release layer that is less prone to static charge.

[0123] One way to evaluate the resistance to static charge is to bring the release layer and surface layer B into contact, apply a load, and then evaluate the amount of charge on the release layer after holding it for a certain period of time. This evaluation method allows for a model-based evaluation of the amount of charge that increases over time when the film is stored in a roll. A detailed evaluation method will be described later.

[0124] The charge of the release layer, as measured by the evaluation method described later, is preferably ±5kV or less, for example, ±3.4kV or less, and more preferably ±3kV or less, with the smaller the absolute value, the better. Setting the charge of the release layer to ±5kV or less is preferable because it reduces the increase in charge over time when the film is stored in roll form, making it difficult for foreign matter to adhere to the film. While a smaller charge of the release layer is preferable, it may be 0.1kV or more, or 0.3kV or more.

[0125] The release film of the present invention may have a functional layer between the substrate and the release layer. Examples of functional layers include, but are not limited to, an antistatic layer and an easily soluble resin layer. Providing an antistatic layer is preferable because it prevents the adhesion of foreign matter due to static charge and suppresses static charge when peeling off ceramic green sheets, thereby achieving stable release properties. Providing an easily soluble resin layer is preferable because it allows for easy separation and removal of the release layer formed on the surface of the release film, and allows for the recovery of only the substrate film with little to no residue of the release layer.

[0126] For example, the release layer substantially does not contain particles with a particle size of 1.0 μm or larger. In this embodiment, particles with a particle size of less than 1.0 μm and 1 nm or larger may be present in the release layer. By substantially not containing inorganic particles with a particle size of 1.0 μm or larger in the release layer, the occurrence of pinholes in ultrathin resin sheets requiring high smoothness, such as ceramic green sheets, can be suppressed, and a resin sheet with a uniform film thickness can be formed. In one embodiment, since it is preferable for the release layer to have high smoothness, it is preferable to provide the release layer according to the present invention on a substrate film having a surface layer A that substantially does not contain inorganic particles, specifically, substantially does not contain particles with a particle size of less than 1.0 μm, preferably a surface layer A that substantially does not contain particles. For example, in a release layer that substantially does not contain particles with a particle size of less than 1.0 μm, it is preferable that it also substantially does not contain particles with a particle size of 1.0 μm or larger. When the release layer is provided on a surface layer A that substantially does not contain inorganic particles (surface layer A of the substrate film), the regional surface roughness (Sa) of the release layer is 3 nm or less, and the maximum protrusion height (P) is 200 nm or less. For example, (Sa) may be 0.1 nm to 3 nm and the maximum protrusion height (P) may be 1 nm to 200 nm, or (Sa) may be 0.2 nm to 3 nm and the maximum protrusion height (P) may be 1 nm to 100 nm. Preferably, the maximum protrusion height (P) may be 1 nm to 50 nm, or 1 nm to 40 nm, or the maximum protrusion height (P) may be 1 nm to 35 nm. By satisfying these conditions, the release layer can suppress the occurrence of pinholes in the thin resin sheet, such as the ceramic green sheet, and a resin sheet with a uniform film thickness can be formed.

[0127] 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. Examples include (4) glycol ethers such as ethers, 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; (5) esters such as ethyl acetate, isopropylene acetate, and N-butyl acetate; (6) ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, isophorone, and diacetone alcohol; and (7) aromatic compounds such as benzene, toluene, and xylene. These can be used individually or in combination of two or more.

[0128] If there is a risk of foreign matter or undissolved particles larger than 1 μm being present in the coating solution, it is preferable to remove them using a filter or the like before application, from the viewpoint of the appearance after application. Various types of filters can be suitably used, but it is preferable to use one that removes 99% or more of particles larger than 1 μm. When a coating solution from which foreign matter and undissolved particles larger than 1 μm have been removed is applied and dried, it is preferable because the occurrence of indentations on the surface of the release layer can be suppressed.

[0129] 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 in terms of productivity, and the amount of solvent remaining in the coating film is small, which is also preferable in terms of long-term stability. 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, the leveling properties are satisfied, and sufficient flatness is obtained, which is preferable. The viscosity of the coating liquid is preferably 10 cps or more and 300 cps or less in terms of the appearance of the coating, and it is preferable to adjust the solid content concentration, organic solvent, etc. so that it falls within this range.

[0130] As a method for laminating the release layer onto a transparent substrate on top of the surface layer by coating, 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, the gravure coating method, particularly the reverse gravure method, is preferred because it allows for uniform coating. Furthermore, the diameter of the gravure is preferably 80 mm or less. A diameter of 80 nm or less is preferable because it suppresses the generation of ridges in the flow direction.

[0131] The following describes in more detail one embodiment of the present invention with reference to examples, but the present invention is not limited thereto. The method for specifying various physical properties in the examples is described below.

[0132] (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 the sample for measurement. Subsequently, the content (ppm) of Sb, Mg, and P elements relative to the mass of the polyester film was determined using an ICP emission spectrometer (Agilent 5900 ICP OES).

[0133] (Number of antimony element-containing protrusions (Sb protrusions) present on the surface of the surface layer) The base film and the release film with the release layer are sized according to the standard paper dimensions of A4 size of the Japanese Industrial Standards (210 mm x 297 mm: area approximately 623.7 cm²) ２A sample was taken from the sample, and the entire area of ​​this sample was visually inspected for foreign matter using the crossed nicol method. Next, each foreign matter detected in the sample was measured from the surface of the surface layer of the sample using a scanning white-light interference microscope (device: Hitachi High-Tech Science Corporation "VertScan" (registered trademark) VS1540) with a 10x objective lens in Phase mode. The obtained microscope image was processed 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 at the surface layer. (Image processing conditions) Image processing was performed in the following order: ・Interpolation: Full interpolation ・Filtering: Gaussian (cutoff 100) ・Surface correction: 4th order

[0134] Furthermore, particle analysis processing was performed under the following conditions, and the number of particles (number of particles) displayed on the "Particle Analysis" screen, which is detected at a height threshold of 25 nm (height threshold setting value: 0.025 μm), was measured. (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)

[0135] Of the protrusions (foreign objects) detected in this analysis, the presence or absence of antimony elements was measured by the following component analysis at locations where protrusions with a height of 0.1 μm or more on the surface of the surface layer were observed.

[0136] (Component analysis of protrusions) Areas where protrusions with a height of 0.1 μm or more were observed were subjected to elemental analysis using a digital microscope (KEYENCE, VHX) equipped with a laser elemental analysis head (KEYENCE, EA-300). The number of protrusions (Sb protrusions) in which antimony element (Sb element) was detected was counted. The number of counted protrusions was measured across the surface observation area (210 mm x 297 mm: area approximately 630 cm²). ２ Divide by ) and the 1 cm present on the film surface ２ The number of protrusions containing antimony element per unit was calculated.

[0137] (Surface layer dissolution) The sample (10 g) obtained by scraping the surface layer was washed with water and dried, and then dissolved in a p-chlorophenol / tetrachloroethane mixture (a solution consisting only of p-chlorophenol and tetrachloroethane, with a mass ratio of p-chlorophenol 3:tetrachloroethane 1) to obtain a dissolution.

[0138] (Filtration of surface layer solution) The surface layer solution was filtered using a membrane filter (Advantec PTFE membrane filter, part number: T050A430A), and the filtered filter was dried to obtain a dried filter. The membrane filter is made of polytetrafluoroethylene, has an average pore size of 0.5 μm, and is circular with a diameter of 47 mm (147.6 mm). ２ ) and its thickness was 90 μm.

[0139] (Total number of particles filtered out by filtration of the dissolution) The dry filter was observed using a scanning electron microscope (SEM) at a magnification of 1,000x, and the number of particles was measured.

[0140] (Number of antimony-containing particles filtered out by filtration of the dissolution and their proportion to the total number of particles) Using a scanning electron microscope (SEM) at a magnification of 1,000x, elemental analysis was performed on the particles on the dry filter, and the number of particles in which Sb was detected (Sb-containing particles) was counted. The proportion (%) of Sb-containing particles was calculated by dividing the number of particles in which Sb was detected by the total number of particles.

[0141] (Amount of Sb element in particles filtered out by filtration of the dissolution) The amount of Sb element per 10 g of surface layer was determined by measuring the particles on the dry filter with fluorescent X-rays, and this was converted to the amount per 1 kg of surface layer (mg).

[0142] (Intrinsic viscosity of surface layer and base film) The intrinsic viscosity was measured (dl / g) in accordance with JIS K 7367-5. For the measurement, a sample obtained by scraping the surface layer or the base film was used, along with 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.

[0143] (Thermal shrinkage rate of the base film in the longitudinal direction) A sample of the base film was taken, measuring 10 mm in width and 220 mm in length. Marks were made at 200 mm intervals along the length of the sample, and the interval between the marks was measured (L0). The sample was then placed between sheets of paper and placed in a hot air oven controlled to 150°C for 30 minutes. After removal, the interval between the marks was measured (L), and the thermal shrinkage rate was calculated using the following formula: Thermal shrinkage rate (%) = {(L0 - L) / L0} × 100

[0144] (Breaking Strength of Base Film) Breaking strength is the stress required for the base film to break. Specifically, a tensile force is gradually applied to the base film, and the force at which the base film breaks is determined. This force is then converted to a stress per unit area (unit: MPa) and expressed as such. Breaking strength was measured in accordance with JIS K 7127, specifically using the following method. A film test piece with a width of 12.7 mm and a length of 200 mm was sampled. The film test piece was set in a tensile testing machine (for example, AG-X manufactured by Shimadzu Corporation), and stretched at a chuck distance of 100 mm and a pull-up speed of 100 mm / min under conditions of 23°C and 65% RH. The breaking strength was calculated from the measured elongation at the time of breakage and the load required for breakage.

[0145] (Surface evaluation of base film for use as a release film in sheet molding) The number of Sb protrusions on the surface of the surface layer is 0.015 per cm. ２ Substrate films with fewer than [number] particles were deemed acceptable and are marked with "○" in Table 4. On the other hand, those that did not meet this condition were deemed unacceptable and are marked with "×" in Table 4. If a film is unacceptable, unevenness may occur when the substrate film is wound onto the roller, or, for example, when the substrate film is used in the manufacture of multilayer ceramic chip capacitors (MLCCs), the frequency of unevenness occurring on the printed surface during printing of internal electrodes may increase.

[0146] (Strength evaluation of base film for use as release film in sheet molding) Base film that has a thermal shrinkage rate in the longitudinal direction of 1.4% or less and a breaking strength of 180 MPa or more is considered acceptable and is indicated as "○" in Table 4. On the other hand, those that do not meet these conditions are considered unacceptable and are indicated as "×" in Table 4. If the base film is unacceptable, breakage, cracking, etc. may occur during the manufacturing or use of the base film, or, for example, dimensional changes may become large when heating to form dielectric sheets and internal electrodes when the base film is used in the manufacture of multilayer ceramic chip capacitors (MLCCs).

[0147] (Overall evaluation of base film for use as release film in sheet molding) If the film passed both the surface evaluation and strength evaluation, it was evaluated as passing overall and marked with "〇" in Table 4. On the other hand, if the film failed either or both of the surface evaluation and strength evaluation, it was evaluated as failing overall and marked with "×" in Table 4.

[0148] (Surface Free Energy) Under conditions of 25°C and 50% RH, droplets of water (droplet volume 1.8 μL), diiodomethane (appropriate liquid volume 0.9 μL), and ethylene glycol (appropriate liquid volume 0.9 μL) were prepared on the release surface of the release film using a contact angle meter (Kyowa Interface Science Co., Ltd.: Fully Automatic Contact Angle Meter DM-701), and the contact angles were measured. The contact angles were taken 10 seconds after dropping each liquid onto the release film. The contact angle data for water, diiodomethane, and ethylene glycol obtained by the above method were calculated using the "Kitazaki-Hata" theory to determine the dispersion component γsd, polar component γsp, and hydrogen bonding component γsh of the surface free energy of the release film, and the sum of these components was defined as the surface free energy γs. This calculation was performed using the calculation software within the contact angle meter software (FAMAS).

[0149] (Surface Roughness) The values ​​were measured using a non-contact surface shape measurement system (VertScan R550H-M100) under the following conditions. The average surface roughness (Sa) of the region was taken as the average of 5 measurements, and the maximum protrusion height (P) was measured 7 times, and the maximum value of 5 measurements was used after excluding the maximum and minimum values. (Measurement Conditions) ・Measurement mode: WAVE mode ・Objective lens: 10x ・0.5x Tube lens ・Measurement area: 936 μm × 702 μm (Analysis Conditions) ・Surface correction: 4th order correction ・Interpolation processing: Full interpolation

[0150] (Evaluation of release properties of ceramic green sheet) A composition consisting of the following materials was stirred and mixed, and dispersed for 60 minutes using a bead mill with zirconia beads with a diameter of 0.5 mm to obtain a ceramic slurry. Toluene 38.3 parts by mass Ethanol 38.3 parts by mass Barium titanate (HPBT-1, manufactured by Fuji Titanium Co., Ltd.) 64.8 parts by mass Polyvinyl butyral (Seslec BM-S, manufactured by Sekisui Chemical Co., Ltd.) 6.5 parts by mass DOP (dioctyl phthalate) 3.3 parts by mass Next, the slurry was applied to the release surface of the obtained release film sample using an applicator so that the dried slurry had a thickness of 0.8 μm, and dried at 60°C for 1 minute to form a ceramic green sheet on the release film. The resulting ceramic green sheet-attached release film was statically removed using a static eliminator (Keyence Corporation, SJ-F020), and then peeled off using a peel tester (Kyowa Interface Science Co., Ltd., VPA-3) at a peel angle of 90 degrees, a peel temperature of 25°C, and a peel speed of 10 m / min. For peeling, double-sided adhesive tape (Nitto Denko Corporation, No. 535A) was attached to a SUS plate attached to the peel tester, and the release film was fixed on top of it with the ceramic green sheet side adhering to the double-sided tape. The release film was then peeled off by pulling it. From the obtained measurements, the average value of the peel force for peel distances of 20 mm to 70 mm was calculated and defined as the peel force. A total of five measurements were taken, and the average value of the peel force was adopted for evaluation. The obtained peel force values ​​were judged according to the following criteria. ○: 0.5 mN / mm or more, 1.0 mN / mm or less △: Greater than 1.0 mN / mm, 2.5 mN / mm or less ×: Greater than 2.5 mN / mm

[0151] (Method for measuring the weight-average degree of polymerization) Analytical conditions 16 mg of the sample was weighed and dissolved in 8 ml of chloroform. The solution was filtered through a 0.2 μm membrane filter, and GPC analysis of the obtained sample solution was performed under the following conditions. Apparatus: TOSOH HLC-8320GPC Column: K-G+ K-802 (exclusion limit molecular weight 5 × 10³) + K-801 (exclusion limit molecular weight 1.5 × 10³) (Shodex), Solvent: 100% chloroform Flow rate: 1.0 ml / min Concentration: 0.2% Injection volume: 50 μL Temperature: 40℃ Detector: RI The weight-average molecular weight was calculated in polystyrene equivalent, and the weight-average degree of polymerization was calculated based on that value. For polystyrene, PStQuick C (TOSOH) from the PStQuick series was used. Of the polystyrenes added to PStQuick C(TOSOH), polystyrenes Mw2110000, 427000, and 37900, which significantly exceed the column's exclusion limit molecular weight, were excluded from the calibration curve.

[0152] (Manufacturing Example 1) <Production of Polyester Resin (Melting Polymerization)> (Slurry Preparation) Terephthalic acid and ethylene glycol were continuously supplied to a slurry preparation tank in a ratio of 100 parts by mass of terephthalic acid to 46.4 parts by mass of ethylene glycol, while stirring under nitrogen flow to prepare the slurry.

[0153] (Esterification Reaction) A continuous esterification reactor consisting of a three-stage complete mixing tank with a stirrer, distillation column, raw material inlet, and product outlet was used as the esterification reactor. Along with the slurry prepared above, an ethylene glycol solution of antimony trioxide (antimony trioxide concentration: 12 g / L) was supplied to the first esterification reactor, 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 solution was removed from the first esterification reactor so that the liquid level remained constant, and then added to the second esterification reactor. Ethylene glycol was added from another inlet of the second esterification reactor 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 solution was removed from the second esterification reactor so that the liquid level remained constant, and then added to the third esterification reactor. In the third esterification reactor, equal amounts of ethylene glycol solution containing magnesium acetate, ethylene glycol solution containing sodium acetate, and ethylene glycol solution containing trimethyl phosphate were added from separate inlets, and the esterification reaction was carried out under atmospheric pressure at a temperature of 260°C with an average residence time of 0.9 hours.

[0154] (Polycondensation reaction) The reaction solution was removed from the third esterification reaction vessel so that the liquid level remained constant, and then added to the first polycondensation reaction vessel of the three-stage continuous polycondensation reactor. 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 vessel so that the liquid level remained constant, and then added to the second polycondensation reaction vessel. 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 reaction vessel so that the liquid level remained constant, and then added to the third polycondensation reaction vessel. The 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 strands, cooled in water, and then cut into pellets.

[0155] <Production of Polyester Resin 1 (Melting Polymerization and Solid-Phase Polymerization)> The polyester resin obtained by melt polymerization was placed in a solid-phase polymerization apparatus. After drying at a temperature of 90°C for 3.5 hours, it was crystallized at a temperature of 130°C for 4.5 hours. Next, the temperature was gradually increased from 197°C to 220°C, and solid-phase polymerization was carried out at a pressure of 40 Pa for 7 hours to obtain polyester resin 1 with an intrinsic viscosity of 0.617 dl / g.

[0156] <Production of Polyester Resins 2-6> Polyester resins 2-6 were obtained in the same manner as polyester resin 1, except that the supply amount of antimony trioxide ethylene glycol solution was changed to match the Sb content (ppm) shown in Table 3, the esterification reaction time and polycondensation reaction time were changed to the times shown in Table 2, and solid-phase polymerization was not performed.

[0157] <Manufacturing of Recycled PET1> 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 put through a single-screw mill and pulverized at a speed of 100 kg / hour through a 4 mm perforated screen to obtain pulverized film. The obtained pulverized film was 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.

[0158] <Manufacturing of Polyethylene Terephthalate / Calcium Carbonate Masterbatch (MB1)> The above polyester resin 4 and calcium carbonate particles with an average particle size of 1.0 μm were melted and kneaded in a twin-screw extruder to produce a masterbatch with a calcium carbonate particle concentration of 20,000 ppm.

[0159] <Manufacturing of Laminated Film X1> After drying polyester resin 1, recycled PET 1, and MB 1, each was melted at 285°C. Using separate melt extruders (290°C), each molten material was filtered in two stages using a filter made of sintered stainless steel fibers with a 95% cut diameter of 15 μm and a filter made of sintered stainless steel particles with a 95% cut diameter of 15 μm. Next, the filtered molten materials were combined in a feed block to laminate a surface layer (layer A), a smooth layer (layer B), and an intermediate layer (layer C), and extruded (casted) into a sheet at a speed of 45 m / min. By electrostatic adhesion and cooling on a casting drum at 30°C, an unstretched laminated polyethylene terephthalate sheet (laminated PET sheet) with an intrinsic viscosity of 0.56 dl / g was obtained. At this time, layer A was formed using only polyester resin 1, and layer B was formed using polyester resin 1 7 The layers were formed by blending 5% by mass of polyester resin 1 and 25% by mass of MB1, and the C layer was formed by blending 60% by mass of polyester resin 1 and 40% by mass of recycled PET 1. The thickness ratio of the layers was adjusted so that A layer / C layer / B layer = 40% / 40% / 20% based on calculations using the discharge rate of each extruder. The electrostatic adhesion conditions at this time were as follows: the electrode material was tungsten, cylindrical (wire) with a diameter of 0.2 mm and a length of 0.5 m, with a constant current control of 5 mA, an electrode tension of 5 kg, and an electrode renewal rate of 5 m / hour.

[0160] Next, the obtained unstretched laminated PET sheet was heated with an infrared heater and then stretched 3.5 times in the longitudinal direction by the speed difference between the rolls at a roll temperature of 80°C. After that, it was guided to a tenter and stretched 4.2 times in the transverse direction at 140°C. Next, it was heat-treated at 210°C in a heat-setting zone. After that, a 2.3% relaxation treatment was performed in the transverse direction at 170°C to obtain a mill roll (width 5.0 m) of laminated biaxially oriented polyethylene terephthalate film (laminated biaxially oriented PET film) with a thickness of 25 μm.

[0161] The obtained mill rolls were moved to a slitter and treated with an anti-static device (Kasuga Electric Co., Ltd., high-density anti-static treatment system) and a web cleaner (Shinko Co., Ltd., ultrasonic cleaner system). After cutting to a width of 1400 mm, a core material with resin-impregnated paper attached, 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, was wound 8000 m in length at a maximum speed of 400 m / min using a contact roll with a rubber hardness of 60 degrees, a contact pressure of 200 kg / m, and a tension of 15 MPa to obtain laminated biaxially oriented PET film rolls. Laminated biaxially oriented PET film (base film) was cut from the obtained rolls and subjected to various evaluations. The evaluation results are shown in Tables 3 and 4.

[0162] <Manufacturing of Laminated Films X2-8> Except for changing the layer configuration, layer thickness ratio, and the types and ratios of constituent resins of layers A-C as shown in Table 1, laminated biaxially oriented PET films were manufactured in the same manner as in Example 1 and subjected to various evaluations. The evaluation results are shown in Tables 3-4.

[0163]

[0164]

[0165]

[0166]

[0167] The base films using polyester resins 1 to 3 in each layer showed excellent results in both surface evaluation and strength evaluation (Examples 1 to 5), confirming their suitability as release sheets useful in the formation of dielectric sheets and printing of internal electrodes in the manufacture of MLCCs. On the other hand, the base films using polyester resins 4 to 6 in each layer lacked performance in either surface evaluation or strength evaluation, failing to achieve a balance between surface performance and strength performance (Comparative Examples 1 to 3), confirming that there is significant room for improvement as release sheets used in the formation of dielectric sheets and printing of internal electrodes in the manufacture of MLCCs.

[0168] (Example 1) A coating solution with the following composition was applied to the surface layer A of a laminated film X1 using reverse gravure so that the release layer thickness after drying was 500 nm, and a release film for manufacturing ultrathin ceramic green sheets was obtained by drying at 120°C for 15 seconds. A ceramic slurry was applied to the obtained release film, and the surface roughness, surface free energy, coating properties, and peelability were evaluated, and good evaluation results were obtained. The composition and various physical properties of the release layer are shown in Tables 5 and 6.

[0169] (Release layer forming composition) Methyl ethyl ketone 44.50 parts by mass Toluene 44.50 parts by mass Melamine compound 9.30 parts by mass (Full ether type methylated melamine, 100% solids, manufactured by Sanwa Chemical Co., Ltd., trade name MW-30M, weight average degree of polymerization 1.3) Release agent 0.50 parts by mass (One-terminated carboxyl-modified polydimethylsiloxane, X22-3710, 100% solids, manufactured by Shin-Etsu Chemical Co., Ltd., alkyl group interposed between dimethylsiloxane and carboxyl group) Acid catalyst 0.20 parts by mass (p-toluenesulfonic acid, manufactured by Hitachi Chemical Co., Ltd., trade name Dryer (registered trademark) 900, 50% solids)

[0170] (Example 2) The release layer was formed in the same manner as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X2.

[0171] (Example 3) The release layer was formed in the same manner as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X3.

[0172] (Example 4) The release layer was formed in the same manner as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X4.

[0173] (Example 5) The release layer was formed in the same manner as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X5.

[0174] (Examples 6-7) The release layer was formed using the same procedure as in Example 1, except that the thickness of the release layer was changed to the value shown in Table 5.

[0175] (Examples 9, 10) The release layer was formed in the same procedure as in Example 1, except that the content of the melamine compound and release agent in the coating solution of Example 1 was changed to the values ​​shown in Table 5.

[0176] (Example 11) A release layer was formed in the same manner as in Example 1, except that the melamine compound in the coating solution of Example 1 was changed to the following composition: (Full ether-type methylated melamine, solids content 70%, manufactured by Sanwa Chemical Co., Ltd., trade name MS-21, weight-average degree of polymerization 1.8)

[0177] (Example 12) A release layer was formed in the same manner as in Example 1, except that the melamine compound in the coating solution of Example 1 was changed to the following composition: (methylol-type methylated melamine, solids content 60%, Sanwa Chemical Co., Ltd., trade name MS-11, weight-average degree of polymerization 1.8)

[0178] (Example 13) A release layer was formed in the same manner as in Example 1, except that the acid catalyst in the coating solution of Example 1 was changed to dinonyl naphthalenedisulfonic acid (manufactured by Kusunoki Chemical Co., Ltd., trade name NACURE® 155, active ingredient 55%).

[0179] (Example 14) A release film for manufacturing ultrathin ceramic sheets was obtained in the same manner as in Example 1, except that the release agent in the coating solution of Example 1 was changed to the following composition: (Side-chain type carboxyl-modified polydimethylsiloxane, X22-3701E, 100% solids, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0180] (Example 15) A release film for manufacturing ultrathin ceramic sheets was obtained in the same manner as in Example 1, except that the release agent in the coating solution of Example 1 was changed to the following composition. The interaction between the hydroxyl group and the melamine compound was strong, and the release force was slightly heavier because the silicone was not exposed on the surface. Polyether-modified OH group-containing polydimethylsiloxane, BYK-377, 100% solids, manufactured by Bic Chemie Japan Co., Ltd.

[0181] (Comparative Example 1) A release layer was formed using the same procedure as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X7. Many antimony-induced protrusions were observed.

[0182] (Comparative Example 2) A release layer was formed in the same manner as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X8. As shown in Table 4, the laminated film X8 has low longitudinal tensile strength, and there is a concern that breakage may occur during release layer processing or, for example, when the release film is used in the manufacture of multilayer ceramic chip capacitors (MLCCs) to form dielectric sheets and internal electrodes.

[0183] (Comparative Example 3) A release layer was formed in the same manner as in Example 1, except that the release agent from the coating solution of Example 1 was removed. The result was poor release properties.

[0184] (Reference Example 1) A release layer was formed using the same procedure as in Example 1, except that a release layer was provided on the surface layer A of the laminated film X6. Many antimony-induced protrusions were observed.

[0185] (Reference Example 2) A release layer was formed in the same manner as in Example 1, except that a release layer with the thickness described in Table 5 was provided on the surface layer A of the laminated film X6. Although there were fewer antimony-induced protrusions, the amount of coating was large and the final release layer thickness was also thick, so it may be necessary to reduce the line speed during the release process compared to the present invention.

[0186]

[0187]

[0188] The embodiments of the present invention exhibit well-balanced physical properties in terms of surface shape, wettability, and release properties, indicating that they can be suitably used in the manufacture of ceramic green sheets. On the other hand, in Comparative Example 1, the polyester film substrate was outside the scope of the present invention, resulting in slightly more pinholes being formed compared to the present invention. In Comparative Example 2, the polyester film substrate was outside the scope of the present invention, raising concerns about breakage during release layer processing or, for example, when the release film is used in the manufacture of multilayer ceramic chip capacitors (MLCCs) to form dielectric sheets and internal electrodes. In Comparative Example 3, the layer corresponding to the release layer did not contain a release agent, resulting in insufficient release properties.

Claims

1. A release film having a polyester film substrate and a release layer, wherein the polyester film substrate is a polyester film comprising a surface layer and a smooth-slip layer containing polyester resin and lubricant particles, the surface layer is made of polyester containing an antimony compound, an alkaline earth metal compound and a phosphorus compound, the intrinsic viscosity of the surface layer is 0.55 or more, the antimony atom content of the surface layer is 120 ppm or less, and the surface free energy of the surface of the release layer is 18 to 35 mJ / m ２ A release film having a release layer thickness of 50 nm to 1500 nm, a regional average surface roughness (Sa) of the surface of the release layer of 7 nm or less, and a maximum protrusion height of 100 nm or less.

2. The number of antimony element-containing protrusions present on the surface of the surface layer of the polyester film substrate is 0.020 per cm. ２ The release film according to claim 1, which is as follows:

3. The release film according to claim 1, wherein the release layer is formed by curing a release layer-forming composition containing a release agent and a melamine compound.

4. The release film according to claim 3, wherein the weight-average degree of polymerization of the melamine compound is 2.0 or less.

5. The release film according to claim 3, wherein the melamine compound content is 80% by mass or more relative to the solid content of the release layer forming composition.

6. The release film according to claim 3, wherein the release agent is a polyorganosiloxane having a functional group that can react with a melamine compound.

7. The release film according to claim 3, wherein the release agent is a polyorganosiloxane containing a carboxyl group.

8. The release film according to claim 1, wherein the intrinsic viscosity of the surface layer is 0.55 to 0.62 dl / g.

9. The number of antimony element-containing protrusions present on the surface of the surface layer is 0.010 per cm. ２ The release film according to claim 1, which is as follows:

10. The release film according to claim 1, wherein the release film is a release film for manufacturing ceramic green sheets or resin sheets.

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