Release film

Abstract

The present invention addresses the problem of providing a release film which can be inhibited from forming transfer marks on the release surface and can diminish winding troubles.　This release film has a release layer including a release surface, a polyester substrate containing substantially no particles, and a projection surface, wherein the projection surface has a maximum projection height Sp of 100 nm or less and the coefficient of dynamic friction between the release surface and the projection surface is 0.2 or higher but less than 1.0.

Description

Release film

[0001] The present invention relates to a release film.

[0002] Polyester films are used in a wide range of applications due to their processability, mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. One application of polyester films is as a release film. Specifically, a release layer is provided on the surface of a polyester substrate, various components are manufactured on the surface of the release layer, and then the components are released. For example, Patent Document 1 discloses a release film for producing ceramic green sheets, which has a polyester substrate and a release layer disposed on one surface of the polyester substrate.

[0003] International Publication No. 2022 / 019113

[0004] The conveying surface of a release film is often provided with protrusions for purposes such as preventing wrinkles during conveyance. However, when the release film is wound into a roll and stored, the protrusions on the conveying surface may be transferred to the release surface, forming transfer marks. The presence of transfer marks on the release surface may reduce the surface smoothness of various components peeled from the release film. In particular, if concave transfer marks are present on the release surface of a release film used to produce a ceramic green sheet, the concave shape may be transferred to the ceramic green sheet, causing variations in the thickness of the ceramic green sheet and potentially affecting the performance of the produced multilayer ceramic capacitor. The inventors further studied release films with reference to the technology described in Patent Document 1 and discovered that in addition to the problem of transfer marks on the release surface, winding failure may occur when the release film is wound into a roll, resulting in a reduction in the quality of the release film.

[0005] In view of the above circumstances, an object of the present invention is to provide a release film that can suppress the formation of transfer marks on the release surface and also suppress winding failures.

[0006] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, they have found that the above problems can be solved by the following configuration.

[0007] [1] A release film having a release layer including a release surface, a polyester substrate that is substantially free of particles, and a protruding surface, wherein the protruding surface has a maximum protrusion height Sp of 100 nm or less, and the dynamic friction coefficient between the release surface and the protruding surface is 0.2 or more and less than 1.0. [2] The release film according to [1], wherein the thickness of the release layer is 2 nm or more and less than 50 nm. [3] The release film according to [1] or [2], wherein the static friction coefficient between the release surface and the protruding surface is 0.2 or more and less than 1.0. [4] The release film according to any one of [1] to [3], wherein the protruding surface has a maximum protrusion height Sp of 35 nm or more and less than 60 nm. [5] The surface free energy of the release surface is 17 to 24 mJ / m ２ [6] The release film according to any one of [1] to [5], wherein the release surface has a maximum projection height Sp of 1 to 30 nm. [7] The release film according to any one of [1] to [6], wherein the release layer contains a silicone resin having a crosslinked structure. [8] The release film according to any one of [1] to [7], wherein the release film has a thickness of 18 to 40 μm. [9] The release film according to any one of [1] to [8], wherein the release film is used for producing a ceramic green sheet.

[0008] According to the present invention, it is possible to provide a release film that can suppress the formation of transfer marks on the release surface and also suppress winding failures.

[0009] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0010] The following describes the meanings of each description in this specification. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, the amount of each component in a composition means the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. Furthermore, in this specification, the amount of each component in each layer or each member means the total amount of the multiple substances present in each layer or each member, unless otherwise specified, when multiple substances corresponding to each component are present in each layer or each member. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0011] In this specification, "longitudinal direction" refers to the longitudinal direction of the film during film production, and is synonymous with "conveyance direction" and "machine direction." In this specification, "width direction" refers to a direction perpendicular to the longitudinal direction. In this specification, "perpendicular" is not limited to strictly perpendicular, but also includes approximately perpendicular. "Approximately perpendicular" means intersecting within a range of 90°±5°, preferably within a range of 90°±3°, and more preferably within a range of 90°±1°.

[0012] In this specification, the weight average molecular weight (Mw) refers to a value measured by gel permeation chromatography (GPC). When the molecular weight is 1,000 or less, the molecular weight is calculated based on the type and number of atoms constituting the compound. Measurement by GPC is performed using an HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) as the measuring device, three TSKgel (registered trademark) Super Multipore HZ-H columns (4.6 mm ID x 15 cm, manufactured by Tosoh Corporation), and THF (tetrahydrofuran) as the eluent. The measurement conditions are a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection volume of 10 μL, and a measurement temperature of 40°C, and is performed using an RI detector. The calibration curve is prepared from eight samples of "Standard Sample TSK Standard, Polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0013] [Release Film] The release film of the present invention (hereinafter also referred to as "the present release film") is a release film having a release layer including a release surface, a polyester base material that is substantially free of particles, and a protruding surface, characterized in that the protruding surface has a maximum protrusion height Sp of 100 nm or less, and the dynamic friction coefficient between the release surface and the protruding surface is 0.2 or more and less than 1.0.

[0014] By having the above-mentioned configuration, this release film can suppress the formation of transfer marks on the release surface and also suppress winding failures. In this release film, by reducing the maximum protrusion height Sp of the protrusion surface, the formation of transfer marks on the release surface when the release film is rolled up and stored can be suppressed. Furthermore, in this release film, by adjusting the dynamic friction coefficient of the release surface within a predetermined range, it is possible to achieve appropriate slip properties even when the maximum protrusion height Sp of the protrusion surface is small, and it is presumed that this is why winding failures can be suppressed.

[0015] The configuration of this release film will be described in detail below.

[0016] <Polyester substrate> The polyester substrate is a film-like object containing a polyester resin as a main component. Here, the "main component" refers to the component that is contained in the largest amount (by mass) of all the components contained in the film-like object.

[0017] The polyester substrate is substantially free of particles. Whether or not a polyester substrate is substantially free of particles can be confirmed by the following procedure. "Substantially free of particles" is defined as the content of particle-derived elements in the polyester substrate being 50 mass ppm or less, preferably 10 mass ppm or less, and more preferably below the detection limit, relative to the total mass of the polyester substrate when the polyester substrate is quantitatively analyzed for particle-derived elements by fluorescent X-ray analysis. This is because even if particles are not actively added to the polyester substrate, contaminants derived from foreign matter, raw material resins, or dirt attached to the line or equipment in the polyester substrate manufacturing process may peel off and be mixed into the polyester substrate. Here, examples of particles include particles (inorganic particles and organic particles) contained in the protrusion-containing layer described below.

[0018] As the polyester substrate, a biaxially oriented polyester substrate is preferred. "Biaxial orientation" refers to the property of having molecular orientation in two axial directions. Molecular orientation is measured using a microwave transmission molecular orientation meter (e.g., MOA-6004, manufactured by Oji Scientific Instruments Co., Ltd.). The angle between the two axial directions is preferably within the range of 90°±5°, more preferably within the range of 90°±3°, and even more preferably within the range of 90°±1°. Molecular orientation changes upon stretching, and a biaxially oriented polyester substrate can be produced by performing biaxial stretching. Preferred embodiments of the polyester substrate include the polyester substrates described in paragraphs

[0021] to

[0039] of the specification of WO 2022 / 019113, the contents of which are incorporated herein by reference.

[0019] (Polyester Resin) The polyester resin contained in the polyester base material is a polymer having an ester bond in the main chain. The polyester resin is usually formed by polycondensation of a dicarboxylic acid compound and a diol compound, which will be described later. There are no particular limitations on the polyester resin, and known polyester resins can be used. Examples of polyester resins include polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), and copolymers thereof. PET, PEN, and copolymers thereof are preferred, and PET is more preferred.

[0020] The intrinsic viscosity of the polyester resin is preferably 0.50 dl / g or more and less than 0.80 dl / g, and more preferably 0.55 dl / g or more and less than 0.70 dl / g. The melting point (Tm) of the polyester resin is preferably 220 to 270°C, and more preferably 245 to 265°C. The glass transition temperature (Tg) of the polyester resin is preferably 65 to 90°C, and more preferably 70 to 85°C.

[0021] The method for producing the polyester resin is not particularly limited, and any known method can be used. For example, the polyester resin can be produced by polycondensing at least one dicarboxylic acid compound and at least one diol compound in the presence of a catalyst.

[0022] The catalyst used for producing the polyester resin is not particularly limited, and any known catalyst that can be used for synthesizing polyester resins can be used. Examples of the catalyst include alkali metal compounds (e.g., potassium compounds, sodium compounds), alkaline earth metal compounds (e.g., calcium compounds, magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, aluminum compounds, germanium compounds, and phosphorus compounds. Among these, titanium compounds or aluminum compounds are preferred because they are less likely to cause foreign matter or voids in the polyester substrate.

[0023] Examples of dicarboxylic acid compounds include dicarboxylic acids such as aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds, as well as dicarboxylic acid esters such as methyl ester compounds and ethyl ester compounds of these dicarboxylic acids. Among these, aromatic dicarboxylic acids or aromatic methyl dicarboxylates are preferred. Examples of aromatic dicarboxylic acid compounds include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic acid. Only one type of dicarboxylic acid compound may be used, or two or more types may be used in combination.

[0024] Examples of diol compounds include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, with aliphatic diol compounds being preferred. Examples of aliphatic diol compounds include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neopentyl glycol, with ethylene glycol being preferred. Examples of alicyclic diol compounds include cyclohexanedimethanol, spiroglycol, and isosorbide. Only one type of diol compound may be used, or two or more types may be used in combination.

[0025] In the production of the polyester resin, a terminal-capping agent may be used as needed. By using the terminal-capping agent, a structure derived from the terminal-capping agent is introduced into the terminal of the polyester resin. For terminal-capping agents, reference may be made to the contents of paragraphs

[0055] to

[0064] of JP 2014-189002 A, the contents of which are incorporated herein by reference.

[0026] As a method for synthesizing the polyester resin, the method described in paragraphs

[0033] to

[0070] of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated herein by reference.

[0027] The content of the polyester resin in the polyester substrate is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the polyester substrate. The upper limit of the content of the polyester resin is not limited and can be appropriately set within a range of less than 100% by mass based on the total mass of the polyester substrate.

[0028] When the polyester base material contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100 mass%, more preferably 95 to 100 mass%, still more preferably 98 to 100 mass%, and particularly preferably 100 mass%, relative to the total mass of the polyester resin in the polyester base material.

[0029] The polyester substrate may contain components other than the polyester resin (for example, a catalyst, unreacted raw material components, particles, water, etc.).

[0030] The thickness of the polyester substrate is preferably 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, and particularly preferably 35 μm or less. The lower limit of the thickness is not particularly limited, but from the viewpoint of improving strength and processability, it is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 10 μm or more, and particularly preferably 20 μm or more. The thickness of the polyester substrate is determined by preparing a slice having a cross section perpendicular to the main surface of the release film and measuring the thickness of five points of the polyester substrate in the slice using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0031] <Release Layer> The release layer is a layer that constitutes the release surface. For example, a member such as a ceramic green sheet is formed on the release surface of the release layer, and the member is peeled from the release surface. The release layer may be provided in direct contact with the polyester substrate, or may be provided via another layer. In order to control the dynamic friction coefficient and static friction coefficient within a predetermined range, it is preferable that the release layer be provided in direct contact with the polyester substrate.

[0032] The release layer preferably contains a release agent. The release agent contained in the release layer is not particularly limited, and examples thereof include silicone resins, fluororesins, alkyd resins, acrylic resins, various waxes, and aliphatic olefin resins. When the release film is a release film for producing a ceramic green sheet as described below, a silicone resin is preferred in terms of the releasability of the ceramic green sheet. The silicone resin refers to a resin having a skeleton (silicone skeleton) containing a siloxane bond in the molecule.

[0033] The release layer preferably has a crosslinked structure in order to maintain the coefficient of friction within a predetermined range, and more preferably contains a silicone resin having a crosslinked structure. Examples of silicone resins having a crosslinked structure include resins obtained by crosslinking using a reactive curable silicone resin. Other examples include resins obtained by crosslinking a silicone-containing resin with a crosslinking agent. Examples of silicone-containing resins include acrylic resins, urethane resins, and olefin resins. Examples of crosslinking agents include oxazoline compounds, carbodiimide compounds, blocked isocyanate compounds, isocyanate compounds, melamine compounds, and epoxy compounds. Among these, oxazoline compounds, carbodiimide compounds, or blocked isocyanate compounds are preferred due to their excellent solvent resistance.

[0034] Examples of reactive curable silicone resins include addition reaction silicone resins, condensation reaction silicone resins, and ultraviolet or electron beam curable silicone resins. Among them, addition reaction silicone resins with low-temperature curing properties, or ultraviolet or electron beam curable silicone resins are preferred because they can form a release layer at low temperatures. Examples of addition reaction silicone resins include resins obtained by reacting polydimethylsiloxane having vinyl groups introduced at the end or side chain with hydrogen siloxane using a platinum catalyst to cure the resin. Examples of condensation reaction silicone resins include resins having a three-dimensional crosslinked structure formed by condensing polydimethylsiloxane having OH groups at the end with polydimethylsiloxane having H groups at the end using an organotin catalyst. Examples of UV-curable silicone resins include those that utilize the same radical reaction as silicone rubber crosslinking, those that are photocured by introducing unsaturated groups, those that use UV or electron beams to decompose onium salts to generate strong acids and then cleave epoxy groups to crosslink, and those that crosslink via an addition reaction of thiol to vinyl siloxane, etc. More specific examples include acrylate-modified polydimethylsiloxane and glycidoxy-modified polydimethylsiloxane.

[0035] The release layer may have a non-silicone resin structure, and preferably contains a non-silicone resin having a crosslinked structure in order to maintain the coefficient of friction within a predetermined range. Examples of non-silicone resins having a crosslinked structure include crosslinked resins obtained by crosslinking a resin (e.g., acrylic resin, urethane resin, olefin resin, etc.) with a crosslinking agent, and crosslinked resins obtained by crosslinking a crosslinking agent. Preferred examples of acrylic resins, urethane resins, and olefin resins are the same as the resins described as the binder contained in the particle-containing layer described below. Examples of crosslinking agents include oxazoline compounds, carbodiimide compounds, blocked isocyanate compounds, isocyanate compounds, melamine compounds, and epoxy compounds. Among them, oxazoline compounds, carbodiimide compounds, or blocked isocyanate compounds are preferred in terms of excellent solvent resistance. The resin contained in the release layer may be used alone or in combination of two or more types.

[0036] The content of the resin in the release layer is preferably 70% by mass or more, more preferably 90% by mass or more, based on the total mass of the release layer. The upper limit is not particularly limited, and may be 100% by mass or less. When multiple types of cured products are contained in the release layer, it is preferable that the total amount is within the above range. The release layer may contain additives in addition to the resin. Examples of additives include surfactants, light release additives and heavy release additives for adjusting the release force, adhesion improvers, and antistatic agents. Examples of surfactants include those contained in the protrusion-containing layer described below, including preferred embodiments.

[0037] (Physical Properties of Release Layer) The thickness of the release layer is not particularly limited, but is preferably 1 to 80 nm. From the viewpoint of better effects of the present invention, it is more preferably 2 nm or more but less than 50 nm, even more preferably 2 to 45 nm, and particularly preferably 2 to 30 nm. The thinner the release layer, the more susceptible the physical properties of the release surface to the influence of the polyester substrate, and therefore it becomes easier to adjust the physical properties such as the elastic modulus of the release surface by using the polyester substrate so that the effects of the present invention are better. The thickness of the release layer is determined by preparing a slice having a cross section perpendicular to the main surface of the release film and measuring it using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and taking the arithmetic average of the thicknesses of five locations on the release layer in the slice.

[0038] In order to smooth the release layer, the maximum protrusion height Sp of the release surface (the surface opposite the polyester substrate) is preferably 1 to 60 nm, more preferably 1 to 30 nm, and even more preferably 1 nm or more but less than 20 nm. The surface average roughness Sa of the release surface is, for example, 0 to 5 nm, and in order to achieve better smoothness, it is preferably 0 nm or more but less than 2 nm, more preferably 0 to 1 nm. The maximum protrusion height Sp and surface average roughness Sa of the release surface can be adjusted by selecting the type of polyester and the type of additive that constitutes the polyester substrate so as to form a smooth film without substantially incorporating particles into the polyester substrate (for example, a method of using a polyester resin polymerized with a titanium compound or an aluminum compound, etc.).

[0039] The maximum protrusion height Sp and surface average roughness Sa of the release surface of the release film are determined by measuring the release surface of the release film using an optical interferometer (e.g., "Vertscan 3300G Lite" manufactured by Hitachi High-Technologies Corporation) and then analyzing the data using the built-in data analysis software. Details of the method for measuring the maximum protrusion height Sp and surface average roughness Sa of the release surface will be described in the Examples below.

[0040] The surface free energy of the release surface is 35 mJ / m in order to prevent static electricity when the release film is wound up. ２ Preferably, 30 mJ / m or less ２ More preferably, 24 mJ / m or less ２The surface free energy of the release surface is more preferably 1 mJ / cm. ２ or more, and from the viewpoint of preventing static electricity when the release film is wound up, 10 mJ / m ２ More than 15 mJ / m is preferable. ２ More preferably, 17 mJ / m or more ２ The surface free energy of the release surface of the release layer can be adjusted by the type of release agent and additives used to form the release layer.

[0041] The method for measuring the surface free energy is as described in the Examples below. The "surface free energy" measured by the method described below is the sum of the polar component and the hydrogen bond component of the surface free energy.

[0042] <Protruding Surface> The present release film has a protruding surface. By having the protruding surface, the present release film has excellent slip properties and excellent transportability.

[0043] In the present release film, the maximum projection height Sp of the protrusion surface is 100 nm or less, and is preferably 1 to 100 nm, more preferably 35 nm or more and less than 60 nm, in order to further suppress the formation of transfer marks.

[0044] In addition, in terms of being able to further suppress the formation of transfer marks, the average surface roughness Sa of the protrusion surface is preferably 1 to 10 nm, more preferably 1 to 8 nm, and even more preferably 1 to 5 nm.

[0045] The maximum projection height Sp and surface average roughness Sa of the protrusion surface can be measured in the same manner as the method for measuring the maximum projection height Sp and surface average roughness Sa of the release surface, except that the protrusion surface is used as the measurement surface. The maximum projection height Sp and surface average roughness Sa of the protrusion surface can be adjusted, for example, by the thickness of the protrusion-containing layer that constitutes the protrusion surface, which will be described later, and the average particle size and content of particles contained in the particle-containing layer that serves as the protrusion-containing layer.

[0046] In the present release film, preferred embodiments regarding the release surface and the protruding surface are shown below. However, the present invention is not limited to the following embodiments. (1) An embodiment in which the maximum projection height Sp of the release surface is 1 to 30 nm and the maximum projection height Sp of the protruding surface is 1 to 100 nm. (2) The embodiment (1) above, in which the maximum projection height Sp of the protruding surface is 35 nm or more and less than 60 nm. (3) The embodiment (1) or (2) above, in which the thickness of the release layer constituting the release surface is 2 nm or more and less than 50 nm (more preferably 2 to 30 nm). (4) Any of the embodiments (1) to (3) above, in which the surface average roughness Sa of the release surface is 0 nm or more and less than 2 nm (more preferably 0 to 1 nm). (5) Any of the embodiments (1) to (4) above, in which the surface average roughness Sa of the protruding surface is 1 to 5 nm.

[0047] The release film may have a protrusion-containing layer as a layer that constitutes the protrusion surface. The protrusion-containing layer may be provided in direct contact with the polyester substrate, or may be provided on the surface of the polyester substrate via another layer. The protrusion-containing layer is preferably provided in direct contact with the polyester substrate.

[0048] The thickness of the protrusion-containing layer is preferably 1 to 500 nm, more preferably 1 to 200 nm, and even more preferably 2 to 100 nm, in order to achieve low haze. The thickness of the protrusion-containing layer is determined by preparing a slice having a cross section perpendicular to the main surface of the release film and measuring the thickness of the protrusion-containing layer at five points in the slice using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0049] The method for forming the protrusion-containing layer is not particularly limited. For example, a method may be used in which a layer containing particles (hereinafter also referred to as a "particle-containing layer") is provided as the protrusion-containing layer on the surface of the polyester substrate opposite to the release layer. Hereinafter, the particle-containing layer as an example of the protrusion-containing layer will be described.

[0050] (Particle-containing layer) The particle-containing layer is a layer containing particles, and preferably contains a resin in addition to particles. The resin can be appropriately selected, for example, a polyester resin may be selected in terms of the recyclability of the release film, or a non-polyester resin other than polyester resin may be selected in terms of better smoothness. Even if the particle-containing layer contains a non-polyester resin other than polyester resin, recycling is possible by peeling the particle-containing layer from the substrate. The particle-containing layer may contain additives other than particles and resin.

[0051] The average particle size of the particles contained in the particle-containing layer is not particularly limited, but is preferably 1 to 250 nm, more preferably 10 to 200 nm, and even more preferably 30 to 130 nm, in terms of better transportability and suppression of transfer marks.

[0052] The particle-containing layer may contain one type of particle or two or more types of particles. When the particle-containing layer contains two or more types of particles with different particle diameters, the particle-containing layer preferably contains at least one type of particle whose average particle diameter is within the above range, and more preferably, all of the two or more types of particles whose average particle diameters are within the above range.

[0053] Examples of particles contained in the particle-containing layer include organic particles and inorganic particles. Resin particles are preferred as organic particles. Examples of resins constituting the resin particles include acrylic resins such as polymethyl methacrylate resin (PMMA), polyester resins, silicone resins, and styrene-acrylic resins. The resin particles may or may not have a crosslinked structure. Specific examples include non-crosslinked acrylic resin particles, non-crosslinked styrene resin particles, crosslinked acrylic resin particles, crosslinked urethane resin particles, and divinylbenzene crosslinked particles. Examples of inorganic particles include silica particles (silicon dioxide particles, colloidal silica), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles).

[0054] The content of particles in the particle-containing layer is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, and even more preferably 1 to 15% by mass, based on the total mass of the particle-containing layer, in terms of better transportability.

[0055] The particle-containing layer preferably contains a binder. Examples of binders include polyester resins and non-polyester resins. Examples of polyester resins include the polyester resins contained in the polyester base material described above. The non-polyester resin is not particularly limited as long as it is a resin other than a polyester resin, but examples include acrylic resins, urethane resins, olefin resins, polyvinyl alcohol resins, and acrylonitrile butadiene resins, and acrylic resins, urethane resins, or olefin resins are preferred. The non-polyester resin may also be an acid-modified resin.

[0056] The acrylic resin is a resin containing structural units derived from (meth)acrylate, and may also contain structural units derived from vinyl monomers such as styrene. The acrylic resin preferably contains structural units derived from (meth)acrylate having an alkyl group containing 1 to 12 carbon atoms, and more preferably contains structural units derived from (meth)acrylate having an alkyl group containing 1 to 8 carbon atoms. In order to suppress the precipitation of impurities such as oligomers contained in the polyester substrate, the acid value of the acrylic resin is preferably 30 mgKOH / g or less, and more preferably 20 mgKOH / g or less. The lower limit of the acid value is not particularly limited and may be, for example, 0 mgKOH / g, but is preferably 2 mgKOH / g or more in terms of coating as an aqueous dispersion.

[0057] The urethane resin is not limited as long as it is a polymer having a urethane bond in its main chain, and known urethane resins such as reaction products of polyisocyanate compounds and polyol compounds can be used. For example, by adjusting the structure and flexibility of the raw polyol compound and polyisocyanate compound, the crosslinking reaction with the organic crosslinking agent can be adjusted, thereby improving the solvent resistance of the release layer. In order to achieve better solvent resistance of the release layer, it is preferable that the urethane resin contain a polyester structure. Commercially available acid group-containing urethane resins include, for example, Hydran (registered trademark) AP-20, AP-40N, and AP-201 (all manufactured by DIC Corporation), Takelac (registered trademark) W-605, W-5030, and W-5920 (all manufactured by Mitsui Chemicals, Inc.), Superflex (registered trademark) 210 and 130, and Elastron (registered trademark) H-3-DF, E-37, and H-15 (all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0058] The olefin resin may be any resin containing structural units derived from an olefin in the main chain. The olefin is not particularly limited, but an alkene having 2 to 6 carbon atoms is preferred, ethylene, propylene, or hexene is more preferred, and ethylene is even more preferred. The olefin-derived structural units contained in the olefin resin preferably account for 50 to 99 mol %, more preferably 60 to 98 mol %, of all structural units in the olefin resin.

[0059] Examples of the acid group-containing olefin resin include copolymers obtained by modifying the above-mentioned olefin resin with an acid-modifying component such as an unsaturated carboxylic acid or an anhydride thereof. Commercially available products of the acid group-containing olefin resin include the ZAIXXEN (registered trademark) series (manufactured by Sumitomo Seika Chemicals Co., Ltd.) such as ZAIXXEN AC, A, L, NC, and N, the CHEMIPEARL (registered trademark) series (manufactured by Mitsui Chemicals, Inc.) such as CHEMIPEARL S100, S120, S200, S300, S650, and SA100, and the HI-TECH (registered trademark) series (manufactured by Toho Chemicals Co., Ltd.) such as HI-TECH S3121 and S3148K. Examples of suitable resins include Arrowbase (registered trademark) series (manufactured by Unitika Ltd.), Arrowbase SE-1013, SE-1010, SB-1200, SD-1200, SD-1200, DA-1010, and DB-4010 (manufactured by Unitika Ltd.), Hardlen AP-2, NZ-1004, and NZ-1005 (manufactured by Toyobo Co., Ltd.), and Sepolsion G315 and VA407 (manufactured by Sumitomo Seika Chemicals Co., Ltd.). Acid-modified olefin resins described in paragraphs

[0022] to

[0034] of JP 2014-076632 A can also be preferably used.

[0060] The binder contained in the particle-containing layer may have a crosslinked structure. That is, the particle-containing layer may be a crosslinked film. The content of the binder contained in the particle-containing layer is preferably 30 to 99.8% by mass, more preferably 50 to 99.5% by mass, based on the total mass of the particle-containing layer.

[0061] The particle-containing layer may contain additives other than the above-mentioned particles and non-polyester resin, such as surfactants, waxes, antioxidants, ultraviolet absorbers, colorants, reinforcing agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, and antifungal agents.

[0062] The particle-containing layer preferably contains a surfactant, since this improves the smoothness of regions other than those where protrusions formed by particles are present. By improving the smoothness of these regions and reducing surface roughness due to factors other than particles, the maximum protrusion height (Sp) of the protrusion surface can be easily controlled within a desired range. The surfactant is not particularly limited, and examples include silicone-based surfactants, fluorine-based surfactants, and hydrocarbon-based surfactants, with hydrocarbon-based surfactants being preferred. Preferred examples of hydrocarbon-based surfactants include polyalkylene oxide compounds and acetylene compounds. One type of surfactant may be used, or two or more types may be used in combination. The content of the surfactant is preferably 0.1 to 10% by mass, based on the total mass of the particle-containing layer, and more preferably 0.1 to 5% by mass, in terms of achieving better surface smoothness.

[0063] The particle-containing layer can be formed, for example, by applying a composition containing particles to one surface of a polyester substrate, or by co-extruding the polyester substrate and the resin used to form the particle-containing layer.

[0064] <Physical Properties of Release Film> In the present release film, the coefficient of dynamic friction between the release surface and the protrusion surface is 0.2 or more and less than 1.0. The coefficient of dynamic friction between the release surface and the protrusion surface is preferably 0.2 to 0.7, and more preferably 0.2 to 0.6, in terms of better effects of the present invention.

[0065] The coefficient of static friction between the release surface and the protrusion surface of the present release film is not particularly limited, but in terms of better effects of the present invention, it is preferably 0.2 or more and less than 1.0, more preferably 0.2 to 0.7, even more preferably 0.2 to 0.6, and particularly preferably 0.2 to 0.5.

[0066] The dynamic and static coefficients of friction between the release surface and the protrusion surface of a release film can be measured in accordance with ASTM-D1894 (1999). Specific measurement methods are as described in the Examples below. The dynamic and static coefficients of friction can be adjusted, for example, by selecting the thickness of each layer of the release film, the type and amount of components such as resin and surfactant contained in each layer, the presence or absence and degree (hardness) of a crosslinked structure in each layer, the type of layer adjacent to each layer, and the number and shape (sharp or smooth) of the protrusions present on the protrusion surface.

[0067] The thickness of the present release film is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 40 μm or less, and particularly preferably 35 μm or less, from the viewpoint of excellent cost efficiency. The lower limit of the thickness is not particularly limited, but from the viewpoint of improved strength and improved processability, it is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 10 μm or more, and particularly preferably 18 μm or more. The thickness of the present release film is measured at five different arbitrarily selected locations using a stylus film thickness meter, and the arithmetic average of the measured values ​​obtained is used.

[0068] The present release film may have layers other than the release layer, polyester substrate, and protrusion-containing layer. Examples of such layers include an intermediate layer disposed between the release layer or the protrusion-containing layer and the polyester substrate. In terms of achieving better effects of the present invention, the present release film is preferably a laminated film consisting of the release layer, polyester substrate, and protrusion-containing layer without the above-mentioned other layers.

[0069] [Manufacturing Method] The manufacturing method of the present release film is not particularly limited as long as it can manufacture a release film having the above-mentioned configuration. For example, a polyester resin is melt-extruded to prepare an unstretched polyester substrate, and then the unstretched polyester substrate is longitudinally stretched. A protrusion-containing layer-forming composition is applied to one side of the uniaxially stretched polyester substrate, and a release layer-forming composition is applied to the other side of the polyester substrate. Next, the obtained polyester substrate with double-sided coating layers is transversely stretched to manufacture the present release film. That is, a manufacturing method including a longitudinal stretching step of longitudinally stretching the unstretched polyester substrate, a protrusion-containing layer-forming step of forming a protrusion-containing layer, a release layer-forming step of forming a release layer, and a transverse stretching step of transversely stretching the polyester substrate can be exemplified.

[0070] The longitudinal stretching can be carried out, for example, by conveying the unstretched polyester substrate in the machine direction while applying tension between two or more pairs of stretching rolls arranged in the conveying direction. The stretching ratio in the longitudinal stretching step is appropriately set depending on the application, but is preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, and even more preferably 2.8 to 4.0 times.

[0071] The protrusion-containing layer-forming composition is not particularly limited as long as it is a composition that can form the protrusion-containing layer described above. Examples of the protrusion-containing layer-forming composition include a composition containing particles contained in the particle-containing layer and a resin. The protrusion-containing layer-forming composition may contain a crosslinking agent. Known crosslinking agents can be used as the crosslinking agent. The protrusion-containing layer-forming composition may contain a solvent. Examples of the solvent include water and organic solvents such as ethanol.

[0072] The method for applying the protrusion-containing layer-forming composition is not particularly limited, and known methods can be used. Examples of application methods include spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating. As an application method, it is preferable to apply an in-line coating method in which the protrusion-containing layer-forming composition is applied to one surface of the longitudinally stretched polyester substrate while transporting the longitudinally stretched polyester substrate. As an application method, it is also possible to apply an offline coating method in which the protrusion-containing layer-forming composition is applied to one surface of a biaxially stretched polyester substrate.

[0073] The composition for forming release layer is not particularly limited as long as it can form the above-mentioned release layer.The composition for forming release layer can be, for example, the composition that contains the above-mentioned release agent, and from the viewpoint of manufacturing suitability, the composition that contains reactive curable silicone resin is preferred.The composition for forming release layer can also contain solvent.

[0074] The coating method of the release layer-forming composition can be the same as the coating method of the protrusion-containing layer-forming composition.As the coating method, it is preferable to apply an in-line coating method in which the release layer-forming composition is applied to one surface of the longitudinally stretched polyester substrate while conveying the longitudinally stretched polyester substrate.As the coating method, it is also possible to apply an off-line coating method in which the release layer-forming composition is applied to the surface of the biaxially stretched polyester substrate opposite to the protrusion-containing layer.

[0075] Transverse stretching is a treatment in which the longitudinally stretched polyester base material is stretched in the width direction.

[0076] The manufacturing method may include other processes in addition to the longitudinal stretching process, the layer formation process, and the transverse stretching process. The manufacturing method according to this embodiment may include at least one process selected from the group consisting of, for example, a heat setting process in which a biaxially stretched polyester substrate is heated and heat set, a heat relaxation process in which the polyester substrate heat-set in the heat setting process is heated at a temperature lower than that in the heat setting process and heat-relaxed, a cooling process in which the polyester substrate heat-relaxed in the heat relaxation process is cooled, and an expansion process in which the heat-relaxed polyester substrate is expanded in the width direction in the cooling process. Specifically, the conditions described in paragraphs

[0085] to

[0165] of WO 2023 / 281972 are preferably exemplified.

[0077] In the above-mentioned method for producing a release film, the protrusion-containing layer is formed by applying a protrusion-containing layer-forming composition in the protrusion-containing layer-forming step, but the method for forming the protrusion-containing layer is not limited to the above embodiment, and any known method can be used. For example, there is a method of forming an unstretched polyester base material laminated with a protrusion-containing layer by co-extrusion molding.

[0078] [Uses] The present release film can be used in a variety of applications. For example, the present release film is preferably used as a release film (carrier film) for producing ceramic green sheets. Ceramic green sheets produced using the present release film can be suitably used in the production of ceramic capacitors, which require multilayer internal electrodes in response to miniaturization and increased capacity. In particular, the present release film suppresses transfer marks from being formed on the release surface. Therefore, when ceramic green sheets are produced using the present release film, variations in the thickness of the ceramic green sheets due to transfer marks can be suppressed, thereby improving the performance of multilayer ceramic capacitors produced using the ceramic green sheets.

[0079] The method for producing a ceramic green sheet using this release film is not particularly limited and can be carried out by a known method. Examples of methods for producing a ceramic green sheet include a method in which a prepared ceramic slurry is applied to the release surface of this release film and the solvent contained in the ceramic slurry is dried and removed. The method for applying the ceramic slurry is not particularly limited, and known methods can be applied, such as a method in which a ceramic slurry obtained by dispersing ceramic powder and a binder in a solvent is applied by a reverse roll method and the solvent is removed by heating and drying. The binder is not particularly limited, and examples thereof include polyvinyl butyral. The solvent is also not particularly limited, and examples thereof include ethanol and toluene.

[0080] The produced ceramic green sheet is used to manufacture a ceramic capacitor. Known methods can be used to manufacture a ceramic capacitor using a ceramic green sheet, including, for example, the following method. First, internal electrodes are provided on a laminate of the present release film and ceramic green sheets by coating or printing a conductive paste. Next, the present release film is removed from the laminate, and ceramic green sheets with internal electrodes are sequentially stacked. The resulting laminate is pressed to produce an intermediate laminate. The intermediate laminate is cut into a desired shape, and the cut intermediate laminate is fired to obtain a ceramic element. Next, external electrodes electrically connected to the internal electrodes are formed on each of the two end faces of the fired intermediate laminate using a conductive paste such as silver, thereby obtaining a ceramic capacitor.

[0081] This release film can also be used as a protective film for dry film resists, a film for sheet molding such as decorative layers and resin sheets, a release film for process manufacturing such as semiconductor manufacturing processes, polarizing plate manufacturing processes and battery manufacturing processes, and a separator for adhesive films for labels, medical and office supplies, etc.

[0082] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below. Unless otherwise specified, "parts" and "%" are based on mass.

[0083] [Film Preparation] First, the procedure for preparing the films used in each example will be described. The physical properties of each film and the methods for measuring the physical properties of the materials used in the film preparation will be described later.

[0084] Example 1 With reference to the conditions described in paragraphs

[0160] to

[0169] of WO 2020 / 158316, the obtained unstretched polyester film was longitudinally stretched. The following protrusion-containing layer-forming composition X1 (composition X1) was applied to one side of the film, and the following release layer-forming composition A1 (composition A1) was applied to the opposite side. The formed coating film was dried with hot air at 100 ° C. to form a protrusion-containing layer and a release layer. That is, composition X1 and composition A1 were applied in-line. At this time, the coating amounts of composition X1 and composition A1 were adjusted so that the thickness of the protrusion-containing layer was 60 nm and the thickness of the release layer was 15 nm. When preparing each composition, the components were mixed, and then filtration was performed using a filter having a pore size of 6 μm (F20, manufactured by Mahle Filter Systems Co., Ltd.) and membrane degassing (2x6 Radial Flow Superphobic, manufactured by Polypore Co., Ltd.) was performed. The obtained film with the coating layer was stretched to prepare a release film, and the prepared release film was wound up in 7000 m increments without knurling under conditions of a tension of 40 kg / m and a touch roll pressure of 25 kg / m. The thickness of the prepared release film was 31 μm (including the 60 nm thick protrusion-containing layer).

[0085] (Protrusion-Containing Layer Forming Composition X1) Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Chemicals Co., Ltd., aqueous dispersion prepared by adding water to a solid content of 25% by mass): 157 parts Anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, water dilution with a solid content of 1% by mass): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion with a solid content of 40% by mass): 14 parts Water: 776 parts

[0086] (Release Layer Forming Composition A1) Emulsion (I) and emulsion (II) were prepared according to the following procedure. (A) 50 parts by mass of a vinyl-containing polydimethylsiloxane in which both ends are each capped with a dimethylvinylsilyl group, (B) 0.5 parts by mass of a platinum-vinylsiloxane complex solution having a platinum content of 1% by mass, (C) 0.11 parts by mass of 1-ethynyl-1-cyclohexanol (manufactured by Nissin Chemical Industry Co., Ltd.), (D) 6.6 parts by mass of a nonionic surfactant ("Naroacty CL-95" manufactured by Sanyo Chemical Industries, Ltd.), and (E) 44 parts by mass of purified water were mixed and stirred to prepare emulsion (I). The platinum content was 100 ppm by mass relative to the mass of polydimethylsiloxane (A). Furthermore, 35 parts by mass of (F) a methylhydrogenpolysiloxane having SiH groups in its side chains and both molecular chain terminals blocked with trimethylsiloxy groups, 5 parts by mass of (G) a nonionic surfactant ("Naroacty CL-95" manufactured by Sanyo Chemical Industries, Ltd.), and 60 parts by mass of (H) purified water were mixed and stirred to prepare emulsion (II). Next, emulsion (I) and emulsion (II) were mixed and further diluted with purified water to a solids concentration of 40% by mass, thereby obtaining a composition. When preparing the composition, the mixing ratio of emulsion (I) and emulsion (II) was adjusted so that the ratio of the total number of moles of SiH groups in component (F) to the total number of moles of alkenyl groups in component (A) was 2.9. To 92.5 parts by mass of the above composition (37 parts by mass in terms of solid content), 5 parts by mass of a silane coupling agent (KBE-403, manufactured by Shin-Etsu Chemical Co., Ltd.) and 2 parts by mass of a nonionic surfactant ("Naloacty CL-95" manufactured by Sanyo Chemical Industries, Ltd.) were added and mixed, and the mixture was further diluted with purified water to a solid content concentration of 1% by mass, thereby obtaining composition A1.

[0087] [Examples 2 to 4] Release films of Examples 2 to 4 were prepared in the same manner as in Example 1, except that the coating amount of Composition A1 was adjusted so that the thickness of the release layer would be the thickness shown in Table 1 below.

[0088] Example 5 A release film of Example 5 was produced in the same manner as in Example 1, except that composition X2 for forming a protrusion-containing layer was used instead of composition X1. The composition of composition X2 for forming a protrusion-containing layer is shown below.

[0089] (Protrusion-Containing Layer Forming Composition X2) Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Chemicals Co., Ltd., aqueous dispersion prepared by adding water to a solid content of 25% by mass): 157 parts Anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, water dilution with a solid content of 1% by mass): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion with a solid content of 40% by mass): 22 parts Water: 776 parts

[0090] Examples 6 to 8 Release films of Examples 6 to 8 were produced in the same manner as in Examples 2 to 4, except that protrusion-containing layer-forming composition X3 was used instead of composition X1. The composition of protrusion-containing layer-forming composition X3 is shown below.

[0091] (Protrusion-containing layer-forming composition X3) - 167 parts of aqueous dispersion (solid content concentration 27.5% by mass) of acrylic resin (acrylic resin copolymerized with a composition of methyl methacrylate / styrene / 2-ethylhexyl acrylate / 2-hydroxyethyl methacrylate / acrylic acid = 59:8:23:5:5 (mass ratio)) - 0.7 parts of nonionic surfactant (Naloacty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content 100% by mass) - 55.7 parts of anionic surfactant (Rapisol A-90, manufactured by NOF Corporation, solid content 1% by mass, diluted with water) - 7 parts of carnauba wax dispersion (Cellosol 524, manufactured by Chukyo Yushi Co., Ltd., solid content 30% by mass) - 20.9 parts of carbodiimide compound (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content 10% by mass, diluted with water) Particles (Snowtex XL, manufactured by Nissan Chemical Industries, Ltd., solid content 40% by mass) 2.8 parts Agglomerated particles (Aerosil OX50, manufactured by Nippon Aerosil Co., Ltd., solid content 10% by mass, water dispersion, median diameter 0.2 μm) 2.95 parts Water 743 parts

[0092] Example 9 A release film of Example 9 was produced in the same manner as in Example 2, except that composition X4 for forming a protrusion-containing layer was used instead of composition X1. The composition of composition X4 for forming a protrusion-containing layer is shown below.

[0093] (Protrusion-Containing Layer Forming Composition X4) Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Chemicals Co., Ltd., aqueous dispersion prepared by adding water to a solid content of 25% by mass): 157 parts Anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, water dilution of 1% by mass solid content): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion of 40% by mass solid content): 11 parts Oxazoline compound (Epocross (registered trademark) WS-700, manufactured by Nippon Shokubai Co., Ltd., aqueous solution with a solid content of 25% by mass): 15 parts by mass Water: 776 parts

[0094] Example 10 A release film of Example 10 was produced in the same manner as in Example 2, except that composition A2 for forming a release layer was used instead of composition A1. The method for preparing composition A2 for forming a release layer is shown below.

[0095] (Release Layer-Forming Composition A2) A composition A2 was obtained in the same manner as for the release layer-forming composition A1, except that the silane coupling agent was not added.

[0096] [Comparative Example 1] According to the method described in paragraphs

[0190] to

[0198] (Example 1), paragraphs

[0227] and

[0229] of WO 2022 / 019113, a release film of Comparative Example 1 having a release layer, a polyester substrate, and a protrusion-containing layer in this order was produced. The composition of the release layer-forming composition A2 used in Comparative Example 1 is shown below, and the thickness of the release layer in the release film of Comparative Example 1 is shown in Table 1. The thickness of the protrusion-containing layer was 60 nm.

[0097] (Release layer-forming composition A3) Addition reaction type silicone (SRX-345, release agent, manufactured by Toray Dow Corning Co., Ltd.): 10 parts Mixed solvent of toluene and methyl ethyl ketone (mixing ratio = 7:3 (mass ratio)): 490 parts Platinum catalyst (SRX-212, manufactured by Toray Dow Corning Co., Ltd.): 0.1 part

[0098] Comparative Example 2 A release film of Comparative Example 2 was produced in the same manner as in Example 4, except that composition X5 for forming a protrusion-containing layer was used instead of composition X1. The composition of composition X5 for forming a protrusion-containing layer is shown below.

[0099] (Protrusion-containing layer-forming composition X5) - Aqueous dispersion of urethane resin (Superflex (registered trademark) 210, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) with a solid content of 35% by mass: 115 parts by mass - Aqueous dilution of anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, manufactured by NOF Corporation) with a solid content of 1% by mass: 36 parts by mass - Aqueous dispersion of non-crosslinked styrene resin particles (Nipol (registered trademark) UFN1008, manufactured by Zeon Corporation) with a solid content of 20% by mass: 11.2 parts by mass - Aqueous dispersion of particles (PMMA resin particles, MP1000, manufactured by Soken Chemical & Engineering Co., Ltd.) with a solid content of 5% by mass: 179.2 parts by mass - Aqueous solution of crosslinker (oxazoline compound, Epocross (registered trademark) WS-700, manufactured by Nippon Shokubai Co., Ltd.) with a solid content of 25% by mass: 32.2 parts by mass - Water: 622 parts by mass

[0100] [Physical Properties] The following physical properties were measured for each of the release films of Examples 1 to 10 and Comparative Examples 1 and 2. The measurement results are shown in Table 1. The thickness of each of the release films of Examples 1 to 10 was 31 μm (including the thickness of the protrusion-containing layer and the thickness of the release-containing layer).

[0101] <Maximum protrusion height Sp, average surface roughness Sa> The maximum protrusion height Sp and average surface roughness Sa of the protrusion surface of the release film were measured using the following method. The protrusion surface of the release film was measured under the following conditions using an optical interferometer (Vertscan 3300G Lite, manufactured by Hitachi High-Tech Corporation), and then analyzed using the built-in data analysis software (VS-Measure5) to determine the maximum protrusion height Sp and average surface roughness Sa of the protrusion surface. In measuring the maximum protrusion height Sp, the maximum value of the measured values ​​obtained from five measurements at different measurement positions was used, and in measuring the average surface roughness Sa, the average value of the measured values ​​obtained from five measurements at different measurement positions was used. (Measurement conditions) Measurement mode: WAVE mode Objective lens: 50x Measurement area: 186 μm × 155 μm The maximum protrusion height Sp and average surface roughness Sa of the release surface of the release film were measured using the same method.

[0102] <Surface Free Energy> The surface free energy of the release surface of the release film was measured by the following method. Using a contact angle meter (DROPMASTER-501, manufactured by Kyowa Interface Science Co., Ltd.), a droplet was dropped onto the release surface of the produced release film at 25°C, and the contact angle was measured 1 second after the droplet adhered to the release surface. 2 μL of purified water, 1 μL of methylene iodide, and 1 μL of ethylene glycol were used as droplets, and the surface free energy was calculated from the measured contact angles using the Kitazaki-Hata method.

[0103] <Coefficient of Friction> For the release films of the Examples and Comparative Examples, the coefficient of friction between the release surface and the protrusion surface was measured in accordance with ASTM D 1894-95. As a measurement condition, the distance over which the flat indenter was moved in the length direction of the fixed test piece was set to 130 mm. The force required to move the flat indenter (test force) was recorded using a measuring instrument, and a plot was created with the movement distance (unit: mm) on the horizontal axis and the test force (unit: N) on the vertical axis. The static friction coefficient and the kinetic friction coefficient were calculated from the measured values ​​of the test force plotted above. The above operation was repeated five times, and the average values ​​of the kinetic friction coefficient and the static friction coefficient for the five measurements were calculated. In the table below, the average value of the kinetic friction coefficient is shown as the kinetic friction coefficient, and the average value of the static friction coefficient is shown as the static friction coefficient.

[0104] [Evaluation] <Transfer Mark Evaluation 1> The obtained release film was cut into 3.5 cm square pieces, and 10 sheets were stacked with the release surface and the protruding surface in contact to obtain a laminate sample. This sample was kept in an oven at 40°C for 3 days with a load of 84 kg applied. The sample was removed from the oven, and the release film was peeled off one by one from each sample. The release surface of the release film was observed at 20,000x magnification using a scanning electron microscope (SEM, Hitachi High-Tech Corporation, S4700), and the presence of transfer marks was evaluated based on the presence of depressions according to the following criteria.

[0105] (Evaluation Criteria for Transfer Mark Evaluation 1) A: No depressions were observed on the peeled surface, and the surface was smooth. B: Depressions were observed on the peeled surface, and the peeled surface was rough.

[0106] <Transfer Mark Evaluation 2: Evaluation after Long-Term Storage> A long-term storage test was performed in which the prepared release film was stored in a room temperature and normal humidity environment for 3 months. Except for using the release film after storage, the transfer marks formed on the release film were evaluated according to the method described in <Transfer Mark Evaluation 1> above.

[0107] (Evaluation criteria for transfer mark evaluation 2) A: No dents were observed, and the surface was smooth. B: A dent was observed on only one of the ten release films, and the remaining nine had smooth surfaces. C: A dent was observed on two or more of the ten release films, and the surface of the release layer was roughened.

[0108] <Winding Failure> The state of the release film when it was wound up after film formation, and the state of the rolled release film after winding were visually observed, and the ability to suppress winding failure was evaluated according to the following criteria. A: No winding slippage or wrinkles were observed. B: No winding slippage was observed. Also, wrinkles were observed during winding, but no wrinkles were observed in the release film after winding. C: Winding slippage was observed during winding, and winding slippage was also observed in the release film after winding. Or, wrinkles were observed during winding, and wrinkles were also observed in the release film after winding.

[0109] In the table, the "Composition No." column of "Release Layer" indicates the number of the composition for forming the release layer, and the "Composition No." column of "Protrusion-Containing Layer" indicates the number of the composition for forming the protrusion-containing layer. ２ ] column shows the surface average roughness Sa, maximum projection height Sp, and surface free energy of the peeled surface, respectively. The "Sa [nm]" and "Sp [nm]" columns of "Projected surface" show the surface average roughness Sa and maximum projection height Sp of the projected surface, respectively.

[0110]

[0111] As shown in Table 1, it was confirmed that the release film of the present invention can suppress the formation of transfer marks and also suppress winding failures. On the other hand, with the release film of Comparative Example 1, in which the dynamic friction coefficient between the release surface and the protrusion surface is 1.0 or more, wrinkles were confirmed to occur when the release film was wound up, and wrinkles were also confirmed in the release film after winding. Furthermore, with the release film of Comparative Example 2, in which the dynamic friction coefficient between the release surface and the protrusion surface is less than 0.2, winding slippage was confirmed to occur when the release film was wound up, and winding slippage was also confirmed in the release film after winding.

[0112] Furthermore, a comparison of Examples 3, 4, 7, and 8 confirmed that when the thickness of the release layer was 30 nm or less, winding failures were further suppressed.

Claims

1. A release film having a release layer including a release surface, a polyester substrate substantially free of particles, and a protruding surface, wherein the protruding surface has a maximum protrusion height Sp of 100 nm or less, and the dynamic friction coefficient between the release surface and the protruding surface is 0.2 or more and less than 1.

0.

2. The release film according to claim 1, wherein the thickness of the release layer is 2 nm or more and less than 50 nm.

3. A release film according to claim 1 or 2, wherein the static friction coefficient between the release surface and the protrusion surface is 0.2 or more and less than 1.

0.

4. A release film according to claim 1 or 2, wherein the maximum projection height Sp of the projection surface is 35 nm or more and less than 60 nm.

5. The surface free energy of the peeling surface is 17 to 24 mJ / m ２ The release film according to claim 1 or 2, 6. The release film according to claim 1 or 2, wherein the release surface has a maximum projection height Sp of 1 to 30 nm.

7. The release film according to claim 1 or 2, wherein the release layer comprises a silicone resin having a crosslinked structure.

8. The release film according to claim 1 or 2, wherein the thickness of the release film is 18 to 40 μm.

9. The release film according to claim 1 or 2, which is used for producing a ceramic green sheet.

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