Mold release film

Abstract

The present invention provides a mold release film that allows reduced use of organic solvents which are harmful to the human body and the environment, and that achieves both easy peelability of a thin resin sheet, particularly a thin ceramic green sheet, and good wettability. The present invention is a mold release film comprising a release layer on at least one surface of a polyester film. The release layer is formed by reacting and curing an aqueous coating composition containing 10 parts by mass or less of an organic solvent per 100 parts by mass of the total coating composition. The composition comprises (a) a first silicone emulsion having at least two alkenyl groups per molecule, (b) a second silicone emulsion having at least two hydrogen groups per molecule, (c) a substrate adhesivity imparting agent, and (d) a surfactant with a number-average molecular weight of 400 or more.

Description

Release film

[0001] The present invention relates to a release film having a base film and a release layer, and relates to a release film that is useful as a film for various processes.

[0002] Conventionally, release films having a base material such as a polyester film and a release layer laminated thereon have high heat resistance and mechanical properties and are used as process films for producing adhesive sheets, cover films, ceramic green sheets, polymer electrolyte membranes, and other resin sheets. Furthermore, many release layers formed from coating compositions containing silicone have been proposed as release layers for release films because of their good heat resistance and releasability (e.g., Patent Documents 1 to 5).

[0003] The release film is also used as a process film for molding ceramic green sheets, which require high smoothness for multilayer ceramic capacitors, ceramic substrates, etc. In recent years, as multilayer ceramic capacitors have become smaller and have increased capacity, the thickness of ceramic green sheets has also tended to decrease. Ceramic green sheets are molded by coating a slurry containing ceramic components such as barium titanate and a binder resin onto the release layer of a release film and drying the slurry. Electrodes are printed on the molded ceramic green sheets, which are then peeled off from the release film to obtain ceramic green sheets with electrodes. Multilayer ceramic capacitors are then manufactured by laminating, pressing, firing, and applying external electrodes to the resulting ceramic green sheets.

[0004] Patent Document 1 proposes a release film produced by a method (hereinafter referred to as "off-line coating") in which a coating composition containing a polysiloxane having an unsaturated group, a polysiloxane having an Si-H group, a platinum group metal catalyst, etc., and an organic solvent is applied to one side of a biaxially oriented polyester, and then the coating composition is dried and cured by heat treatment to form a release layer.

[0005] Patent Documents 2 and 3 propose release films in which a release layer is formed by applying an aqueous coating composition containing an alkenyl group-containing silicone and an Si—H group-containing silicone to one side of a polyester film, and then stretching the polyester film (hereinafter referred to as “in-line coating”).

[0006] Patent Document 4 proposes a release film in which a release layer is formed by in-line coating of an aqueous coating composition containing an alkenyl group-containing silicone and a silicone containing a hydrogen group and a phenyl group.

[0007] Furthermore, Patent Document 5 proposes a release film using off-line coating.

[0008] International Publication No. WO2017 / 200056 Japanese Patent Application Laid-Open No. 2003-292894 Japanese Patent Application Laid-Open No. 2010-17932 Japanese Patent No. 5735278 Japanese Patent No. 6619200

[0009] In recent years, as ceramic green sheets have become thinner, there has been a trend toward release films with light releasability, allowing the ceramic green sheets to be peeled off with a low and uniform force. Furthermore, there is a demand for release films with good wettability to the ceramic slurry applied to the release layer. To achieve a thinner ceramic green sheet, for example, it is necessary to uniformly apply a diluted ceramic slurry with a low solids concentration onto the release layer using an organic solvent in an amount equal to or greater than the amount of resin. When a ceramic slurry composed of such a composition is applied onto a release layer, the wettability of the release film to the ceramic slurry may be insufficient. Slight repelling or uneven application during application may result in pinholes or thickness variations in the ceramic green sheet, potentially reducing the yield of multilayer ceramic capacitors.

[0010] After extensive research, the inventors discovered that the organic solvent contained in the release layer, which is formed by applying an aqueous coating composition, reacting it, and solidifying it, can also affect the physical properties of the release layer.

[0011] Specifically, the organic solvent impairs the stability of the water-dispersed emulsion contained in the aqueous coating composition, which impairs the uniformity of the release layer formed from the composition and results in poor releasability and other problems.

[0012] Furthermore, the increased amount of organic solvent used increases the risk of harm to the human body and the burden on the environment.

[0013] Furthermore, the release film requires a release layer with good substrate adhesion. For example, if the substrate adhesion of the release layer is insufficient, when peeling off various resin sheets laminated on the release film, a part or most of the release layer may peel off from the substrate, and the components of the release layer may be mixed into the resin sheet. Furthermore, in various resin sheet molding processes, there is a risk of the release layer peeling off from the substrate film during transport of the release film.

[0014] Furthermore, release films are required to have substrate adhesion immediately after the release layer is formed, i.e., immediate adhesion to the substrate. In the case of a release layer that has poor immediate adhesion to the substrate, there is a risk that a portion of the release layer will be transferred to the transport roll during the production process of the release film, or that the release layer will be transferred to the back surface of the release film that comes into contact with the release layer when the release film is wound into a roll. If transfer of the release layer to the transport roll or the back surface of the release film occurs, there is a risk that the coating uniformity of the release layer will deteriorate, the thickness of the release layer will decrease, defects will occur on the surface of the release layer, and heavy release will occur.

[0015] In Patent Document 1, the releasability and wettability of the thin ceramic green sheet are particularly insufficient, and further improvement in both easy releasability and good wettability is required. Furthermore, because a coating composition containing an organic solvent as a main component is used, there are problems with the adverse effects on the human body from contact with the organic solvent or inhalation of its vapor, and with the burden on the global environment from the release of organic solvent vapor into the atmosphere.

[0016] In addition, the drying equipment for organic solvents must be explosion-proof, which requires initial installation costs, and it requires a lot of energy to operate. ２ The problem was that the amount of emissions was large and the environmental impact was significant.

[0017] In Patent Document 2, a release layer is formed using a coating composition that uses toluene, and in Patent Document 3, a release layer is formed using a coating composition that uses a mixed solvent of water and isopropyl alcohol, but these have had issues such as harmfulness to the human body and a large environmental impact.

[0018] Furthermore, non-polar solvents such as toluene and alcohol-based solvents such as isopropyl alcohol can impair the stability of water-dispersed emulsions, causing problems such as a loss of coating uniformity due to emulsion aggregation and gelation, resulting in the occurrence of coating defects such as coarse protrusions and repelling caused by the aggregates. In particular, when forming a release layer using silicone with excellent release properties, it is necessary to use emulsified silicone because silicone is generally insoluble in water, which has created challenges in producing release films with easy release properties.

[0019] The release film described in Patent Document 4 has a release layer formed by in-line coating, but is not intended for use in molding ceramic green sheets, and has issues with the releasability of thin ceramic green sheets in particular. Furthermore, a phenyl group-containing crosslinking agent is used to improve adhesion between the substrate and the release layer, but the effect of the phenyl group on the release force has not been recognized, making it unsuitable for a release film with easy releasability. Furthermore, the release layer has no effect on the substrate adhesion immediately after formation, i.e., immediate adhesion to the substrate, and there is an issue of defects occurring in the release layer during the release film manufacturing process and various resin sheet molding processes, resulting in heavy releasability.

[0020] The release film described in Patent Document 5 has the problems of being harmful to the human body and having a large environmental impact because the composition forming the release layer contains an organic solvent as a main component, as described above. In addition, the biaxially oriented polyester film substrate may be deformed by the heat generated during drying and curing of the coating composition, and therefore the film had to be produced at a relatively low temperature.

[0021] In the invention of Patent Document 5, as described in the examples, the coating composition is cured by heating at 135° C., which may result in an insufficient amount of heat for curing the release layer. If the release layer is not cured sufficiently, the solvent resistance of the release layer is impaired, and the force required to peel the ceramic green sheet increases, which may damage the ceramic green sheet during peeling and cause defects.

[0022] The present invention has been made in view of the problems of the prior art. That is, an object of the present invention is to provide a release film that can reduce the amount of organic solvents that are harmful to the human body and have a negative effect on the environment, achieves both easy releasability and good wettability for a thin resin sheet, particularly a thin ceramic green sheet, and further has improved adhesion, particularly immediate adhesion, between a base film and a release layer.

[0023]

[0003] As a result of extensive investigations, the present inventors have found that a surfactant contained in an aqueous coating composition can adversely affect immediate adhesion to a substrate. Specifically, when the aqueous coating composition dries and solidifies, the surfactant segregates toward the substrate film, impairing the adhesion between the release layer and the substrate film, resulting in a problem of deterioration of immediate adhesion.

[0024] On the other hand, simply removing the surfactant from a release layer formed from an aqueous coating composition may result in insufficient wettability with ceramic slurries and the like, and may not satisfy the required properties of a release film.

[0025] As a result of extensive research to solve the above problems, the present inventors have found that the above object can be achieved by a release film having the following configuration, and have completed the present invention.

[0026] That is, the present invention has the following configurations. [1] A release film having a release layer on at least one surface of a polyester film, the release layer being a layer formed by reacting and solidifying an aqueous coating composition, the aqueous coating composition containing 10 parts by mass or less of an organic solvent per 100 parts by mass of the total amount of the aqueous coating composition, the aqueous coating composition comprising: (a) a first silicone emulsion containing at least two alkenyl groups per molecule, (b) a second silicone emulsion containing at least two hydrogen groups per molecule, (c) a substrate adhesion promoter, and (d) a surfactant having a number average molecular weight of 400 or more. [2] The release film according to [1], wherein the substrate adhesion promoter (c) is a water-soluble or water-dispersible silane coupling agent having a hydrolyzable functional group bonded to a silicon atom directly or via another functional group. [3] The release film according to any one of [1] and [2], wherein the release film is formed by applying the aqueous coating composition to a substrate film before completion of crystal orientation, stretching the substrate film in at least one direction, and then heat-treating the substrate film to complete the crystal orientation of the substrate film. [4] The release film according to any one of [1] to [3], wherein the polyester film has a surface layer that is substantially free of inorganic particles, and the release layer is formed on the surface layer. [5] The release film according to any one of [1] to [4], wherein the release film is a release film for use in manufacturing a multilayer ceramic capacitor or a resin sheet.

[0027] The release film of the present invention can improve the releasability and wettability of the release layer, and can further suppress the occurrence of defects in a thin resin sheet, particularly a ceramic green sheet. Furthermore, a release layer can be formed that is free from the risk of deterioration in the adhesion between the substrate film and the release layer, particularly in the immediate adhesion to the substrate.

[0028] Furthermore, the production process can be less harmful to the human body and less burdensome to the environment, and a uniform release layer can be formed without risking loss of stability of the first silicone emulsion and the second silicone emulsion contained in the aqueous coating composition.

[0029] Furthermore, the present invention can achieve both wettability and releasability of the release layer.

[0030] The present invention has the features described in this specification, and therefore can further solve the problems described below and achieve the effects described below.

[0031] In particular, it is possible to achieve both easy peelability and good wettability for the thin-layer ceramic green sheet. Furthermore, compared with coating compositions containing organic solvents as a main component, the amount of organic solvent can be significantly reduced, or even eliminated entirely. As a result, the adverse effects on the human body caused by contact with organic solvents or inhalation of their vapors, as well as the burden on the global environment caused by the release of organic solvent vapors into the atmosphere, can be significantly reduced.

[0032] Furthermore, there is no need to use explosion-proof equipment for drying organic solvents, and energy consumption during operation can be reduced compared to conventional manufacturing equipment. ２ It also reduces emissions and reduces the burden on the environment.

[0033] Furthermore, the present invention can suppress the aggregation and gelation of the emulsion, thereby achieving excellent coating uniformity, reducing the formation of large protrusions due to aggregates, and suppressing the occurrence of coating defects such as repelling in a balanced manner.In addition, a release film exhibiting easy releasability can be obtained.

[0034] In addition, the present invention allows the reaction and solidification of the coating composition and the stretching and crystallization of the polyester film to proceed simultaneously, thereby allowing the hardening of the release layer to proceed at high temperatures while suppressing thermal deformation of the base polyester film compared to conventional methods.

[0035] Furthermore, since the release layer can be sufficiently cured, the release layer has excellent solvent resistance. Furthermore, for example, the force required to peel the ceramic green sheet can be suppressed from increasing, which reduces damage to the ceramic green sheet during peeling and prevents defects.

[0036] Furthermore, according to the present invention, when an aqueous coating composition is applied onto a polyester film, the occurrence of coating defects such as repelling during the drying process can be suppressed, and coating defects such as uneven thickness of the release layer, the occurrence of coarse protrusions, and coating voids can be suppressed.

[0037] For example, in the present invention, in an embodiment in which a release film is produced using an in-line coating method, a release layer that is excellent in hardening and releasability can be formed, and the required physical properties can also be obtained with respect to the wettability of the ceramic slurry, which has previously been considered difficult.

[0038] Furthermore, according to the present invention, an aqueous coating composition containing a substrate adhesion promoter is used, so that a release film having excellent substrate adhesion can be obtained. In particular, when a coating composition containing a surfactant is used to produce the release film by in-line coating, the surfactant is likely to segregate near the interface between the substrate film and the release layer, and immediate adhesion to the substrate immediately after the release layer is cured is required. According to the present invention, by including the substrate adhesion promoter, a release film having excellent immediate adhesion to the substrate can be obtained.

[0039] The present invention relates to a release film having a release layer on at least one surface of a polyester film, wherein the release layer is formed by reacting and solidifying an aqueous coating composition, and the aqueous coating composition contains an organic solvent in an amount of 10 parts by mass or less per 100 parts by mass of the total amount of the aqueous coating composition, and the composition includes: (a) a first silicone emulsion containing at least two alkenyl groups per molecule; (b) a second silicone emulsion containing at least two hydrogen groups per molecule; (c) a substrate adhesion promoter; and (d) a surfactant having a number average molecular weight of 400 or more.

[0040] The present invention having such a configuration can achieve both easy releasability and good wettability of the release layer, and can provide a thin resin sheet, such as a thin ceramic green sheet, with a uniform thickness without defects, and can suppress defects such as pinholes.

[0041] The present invention can also achieve the following effects: The present invention uses an aqueous coating composition that contains significantly less organic solvent than conventional compositions, or an aqueous coating composition that is substantially free of organic solvents, which reduces the harmful effects on the human body and the environmental impact, and reduces CO ２ It is possible to produce a release film while suppressing the occurrence of

[0042] Furthermore, in one embodiment, the release film of the present invention can achieve both releasability and wettability by forming a release layer by applying an aqueous coating composition having a predetermined composition using an in-line coating method. More specifically, the thermosetting silicone emulsion can be heat-cured in a relatively high-temperature environment, thereby exhibiting excellent releasability. In-line coating allows the substrate film to be stretched and crystallized simultaneously with the formation of the release layer, so that a release film with excellent flatness can be produced without causing deformation or shrinkage of the film due to heat even when exposed to relatively high temperatures, specifically, heat of 180°C or higher.

[0043] Furthermore, by including a substrate adhesion promoter in the aqueous coating composition, a release film with excellent substrate adhesion can be produced. Although the details of why such an effect is obtained are not clear, it is thought that the substrate adhesion promoter segregates toward the substrate film during the process of forming the release layer, and generates hydrogen bonds or covalent bonds between the substrate film and the release layer, thereby exhibiting substrate adhesion. Furthermore, when a silane coupling agent is used as the substrate adhesion promoter, a dehydration condensation reaction occurs between the silane coupling agents, increasing the crosslink density of the release layer and allowing the production of a release film with excellent releasability.

[0044] In addition, because an aqueous coating composition containing a surfactant is used, when the coating composition is applied to a polyester film to form a release layer, there are no coating defects such as repelling, and the release layer has excellent releasability. Furthermore, because the stability of the silicone emulsion is increased, there is no risk of coarse protrusions or uneven thickness of the release layer due to aggregation or gelation of the emulsion.

[0045] Furthermore, by setting the number-average molecular weight of the surfactant to 400 or more, the surfactant does not volatilize during drying and solidification of the aqueous coating composition, allowing the surfactant to remain in the release layer. Generally, surfactants exhibit amphiphilicity, meaning they are compatible with both organic solvents and water. Therefore, the surfactant that is thought to remain in the release layer, particularly on the surface, can provide a release layer with excellent wettability to ceramic slurries and the like. On the other hand, poor solvent resistance to organic solvents in ceramic slurries can lead to increased peel strength. However, by curing the release layer at a relatively high temperature, a release layer with high crosslink density and excellent solvent resistance can be obtained, allowing the production of a release film that exhibits easy peelability and good wettability, which have previously been difficult to achieve. Details regarding surfactants will be discussed later.

[0046] (Polyester Film) The polyester constituting the polyester film used as the base film is not particularly limited, and a film formed from a polyester commonly used as a base material for release films can be used. Preferred are crystalline linear saturated polyesters composed of an aromatic dibasic acid component and a diol component. For example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or copolymers primarily composed of these resin components are even more preferred. Polyester films formed from polyethylene terephthalate are particularly preferred. The polyethylene terephthalate preferably contains 90 mol% or more, more preferably 95 mol% or more, of ethylene terephthalate repeating units, and may be copolymerized with small amounts of other dicarboxylic acid components or diol components. For example, from the standpoint of cost, polyethylene terephthalate produced solely from terephthalic acid and ethylene glycol is preferred. Furthermore, known additives, such as antioxidants, light stabilizers, UV absorbers, and crystallization agents, may be added within limits that do not impair the effects of the release film of the present invention. The polyester film is preferably a biaxially oriented polyester film due to its high bidirectional elastic modulus.

[0047] The intrinsic viscosity of the polyester film is preferably 0.50 dl / g or more and 0.70 dl / g or less, more preferably 0.52 dl / g or more and 0.62 dl / g or less. When the intrinsic viscosity is 0.50 dl / g or more, breakage does not occur frequently during the stretching process, which is preferable. Conversely, when the intrinsic viscosity is 0.70 dl / g or less, cuttability is good when cutting to a predetermined product width, and dimensional defects do not occur, which is preferable. It is also preferable to thoroughly vacuum dry the raw material pellets.

[0048] In this specification, when simply referring to a "polyester film," it means a polyester film having (laminated with) a surface layer A and a surface layer B.

[0049] The method for producing the polyester film of the present invention is not particularly limited, and any conventionally used method can be used. For example, the polyester can be melted in an extruder, extruded into a film, and cooled on a rotating cooling drum to obtain an unstretched film, which can then be biaxially stretched. A biaxially stretched film can be obtained by sequentially biaxially stretching a uniaxially stretched film in the longitudinal or transverse direction, or by simultaneously biaxially stretching an unstretched film in the longitudinal and transverse directions.

[0050] In the present invention, the stretching temperature during stretching of the polyester film is preferably equal to or higher than the second-order transition temperature (Tg) of the polyester. Stretching is preferably performed at a magnification of 1 to 8 times, particularly 2 to 6 times, in both the longitudinal and transverse directions.

[0051] The polyester film preferably has a thickness of 12 μm or more and 50 μm or less, more preferably 15 μm or more and 38 μm or less, and even more preferably 19 μm or more and 33 μm or less. A film thickness of 12 μm or more is preferable because there is no risk of deformation due to heat during film production, processing, or molding. On the other hand, a film thickness of 50 μm or less is preferable because the amount of film discarded after use is not excessively large, thereby reducing the environmental load.

[0052] The polyester film substrate may be a single layer or a multilayer structure of two or more layers. For example, the substrate film may be a polyester film having a surface layer A that is substantially free of particles having a particle size of 1.0 μm or more and a surface layer B that contains particles. Preferably, the surface layer A is substantially free of inorganic particles having a particle size of 1.0 μm or more.

[0053] In this embodiment, particles having a particle size of less than 1.0 μm and 1 nm or more may be present in the surface layer A. When the surface layer A is substantially free of particles having a particle size of 1.0 μm or more, such as inorganic particles, it is possible to reduce defects caused by the shape of particles in the substrate being transferred to the resin sheet.

[0054] In one embodiment, the surface layer A does not contain particles having a particle size of less than 1.0 μm, so that defects caused by the transfer of particle shapes in the substrate to the resin sheet can be more effectively prevented.

[0055] In one embodiment, the polyester film substrate is preferably a laminate film having a surface layer A substantially free of inorganic particles on at least one side. This more effectively prevents defects caused by the transfer of particle shapes in the substrate to the resin sheet. For example, a preferred embodiment is that the surface layer A substantially free of particles having a particle size of less than 1.0 μm also substantially free of particles having a particle size of 1.0 μm or more.

[0056] In the present invention, "substantially free of particles" means, for example, in the case of inorganic particles less than 1.0 μm in size, that the content of inorganic elements quantified by fluorescent X-ray analysis is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit. This is because even if particles are not actively added to the film, contaminants from foreign substances or dirt adhering to the raw resin or the production line or equipment during the film manufacturing process may peel off and be mixed into the film. Furthermore, "substantially free of particles with a particle size of 1.0 μm or more" means that particles with a particle size of 1.0 μm or more are not actively included.

[0057] In the case of a laminated polyester film having a multi-layer structure of two or more layers, it is preferable that a surface layer B that can contain inorganic particles or the like is provided on the surface opposite to a surface layer A that does not substantially contain inorganic particles.

[0058] As for the laminate structure, if the layer on the side to which the release layer is applied is layer A, the layer on the opposite side is layer B, and the other core layer is layer C, the layer structure in the thickness direction can be a laminate structure such as release layer / A / B or release layer / A / C / B. Naturally, layer C may have a multi-layer structure. Furthermore, surface layer B may not contain inorganic particles. In that case, it is preferable to provide a coating layer containing at least inorganic particles and a binder on surface layer B to impart slip properties for winding the film into a roll.

[0059] In the polyester film substrate of the present invention, the surface layer B, which forms the surface opposite to the surface to which the release layer is applied, preferably contains inorganic particles, and in particular, silica particles and / or calcium carbonate particles, from the viewpoint of the slipperiness of the film and ease of air escape. The content of the inorganic particles contained in the surface layer B is preferably 5,000 ppm or more and 15,000 ppm or less in total.

[0060] In this case, the area surface average roughness (Sa) of the film of the surface layer B is preferably in the range of 1 nm to 40 nm. More preferably, it is in the range of 5 nm to 35 nm. When the total content of silica particles and / or calcium carbonate particles is 5,000 ppm or more and Sa is 1 nm or more, air can be uniformly released when the film is wound into a roll, resulting in a good wound shape and good flatness, making it suitable for producing ultrathin ceramic green sheets. Furthermore, when the total content of silica particles and / or calcium carbonate particles is 15,000 ppm or less and Sa is 40 nm or less, the lubricant is less likely to aggregate and large protrusions are not formed, which is preferable because it ensures stable quality when producing ultrathin ceramic green sheets.

[0061] In addition to silica and / or calcium carbonate, inactive inorganic particles and / or heat-resistant organic particles can also be used as particles contained in Layer B. However, from the viewpoints of transparency and cost, it is more preferable to use silica particles and / or calcium carbonate particles. Other inorganic particles that can be used include alumina-silica composite oxide particles and hydroxyapatite particles. Heat-resistant organic particles include crosslinked polyacrylic particles, crosslinked polystyrene particles, and benzoguanamine particles. When silica particles are used, porous colloidal silica is preferred, and when calcium carbonate particles are used, light calcium carbonate that has been surface-treated with a polyacrylic acid-based polymer compound is preferred from the viewpoint of preventing the lubricant from falling off.

[0062] The average particle size of the inorganic particles added to the surface layer B is preferably 0.1 μm or more and 2.0 μm or less, particularly preferably 0.5 μm or more and 1.0 μm or less. If the average particle size of the inorganic particles is 0.1 μm or more, the slipperiness of the release film is good, which is preferable. Furthermore, if the average particle size is 2.0 μm or less, there is no risk of adversely affecting the smoothness of the release layer surface, and there is no risk of pinholes occurring in the ceramic green sheet, which is preferable.

[0063] It is preferable to provide a release layer on the surface layer A. From the viewpoint of reducing pinholes, it is preferable that recycled raw materials or the like are not used for the surface layer A, which is the layer on which the release layer is to be provided, in order to prevent the inclusion of inorganic particles such as lubricants.

[0064] The thickness ratio of the surface layer A, which is the layer on which the release layer is provided, is preferably 20% to 50% of the total layer thickness of the base film. If it is 20% or more, the film is less likely to be affected from the inside by particles contained in the surface layer B, etc., and it is easy for the regional surface average roughness Sa to satisfy the above range, which is preferable. If it is 50% or less of the total layer thickness of the base film, the proportion of recycled raw materials used in the surface layer B can be increased, which is preferable as it reduces the environmental load.

[0065] From the viewpoint of economic efficiency, recycled raw materials such as film scraps and PET bottles may be used in an amount of 50% by mass to 90% by mass for the layers (surface layer B or the aforementioned intermediate layer C) other than the surface layer A. Even in this case, it is preferable that the type and amount of the lubricant contained in layer B, its particle size, and the area surface average roughness (Sa) satisfy the above-mentioned ranges.

[0066] Furthermore, in order to improve the adhesion of a release layer or the like to be applied later, or to prevent static charging, a coating layer may be provided on the surface of the surface layer A and / or the surface layer B before stretching or after uniaxial stretching in the film-forming process, or a surface treatment may be applied.

[0067] In one embodiment, the release layer-forming surface to which the aqueous coating composition is applied can be subjected to a surface treatment or provided with an easy-adhesion layer in order to enhance adhesion to the release layer. Examples of surface treatments include plasma treatment, corona discharge treatment, ultraviolet treatment, flame treatment, and electron beam / radiation treatment. Examples of the easy-adhesion layer include a layer containing the same resin as the substrate film and further containing an antistatic agent, a pigment, a surfactant, a lubricant, an antiblocking agent, etc. When an adhesion improver such as a coupling agent is added to the aqueous coating composition, the release layer can have sufficient adhesion to the substrate film even without providing an easy-adhesion layer, etc.

[0068] (Release Layer) In the present invention, the release layer is preferably laminated on the surface layer A of the substrate film. In the present invention, the release layer is a layer formed by reacting and solidifying an aqueous coating composition, and the aqueous coating composition contains an organic solvent in an amount of 10 parts by mass or less relative to 100 parts by mass of the total amount of the coating composition, and is formed from an aqueous coating composition containing: (a) a first silicone emulsion containing at least two or more alkenyl groups per molecule; (b) a second silicone emulsion containing at least two or more hydrogen groups per molecule; (c) a substrate adhesion promoter; and (d) a surfactant having a number average molecular weight of 400 or more.

[0069] The release layer having such characteristics can provide a release film with excellent releasability and wettability, can suppress the occurrence of defects such as pinholes in the resin sheet or ceramic green sheet, and can form a sheet with a uniform thickness. In addition, the release film can have excellent immediate adhesion to the substrate.

[0070] More specifically, since the release layer is formed by in-line coating in the present invention, the release layer can be cured without impairing the flatness of the release film even in a relatively high temperature environment of 180° C. or higher. Therefore, a release layer with a higher crosslink density than that formed by conventional off-line coating can be formed, and light releasability can be achieved.

[0071] Furthermore, according to the present invention, it is possible to produce a release layer containing a surfactant that is compatible with water and organic solvents, and to have excellent wettability when forming a sheet from a ceramic slurry, etc. Furthermore, it is possible to increase the stability of the silicone emulsion that forms the release layer, and to obtain a release film having a uniform release layer without coating defects.

[0072] Furthermore, even if the surfactant remains in the release layer, the adhesion to the substrate is not deteriorated, and a release film having excellent immediate adhesion to the substrate can be obtained.

[0073] The aqueous coating composition forming the release layer contains an organic solvent in an amount of 10 parts by mass or less per 100 parts by mass of the total amount of the coating composition.

[0074] By satisfying the above-mentioned conditions for the amount of organic solvent contained in the composition, it is possible to significantly reduce the amount of organic solvent, or to make the composition substantially free of organic solvent, compared with coating compositions containing organic solvents as a main component, thereby significantly reducing the adverse effects on the human body caused by contact with organic solvents or inhalation of their vapors, and the burden on the global environment caused by the release of organic solvent vapors into the atmosphere.

[0075] In one embodiment, the aqueous coating composition may contain an organic solvent in an amount of 0.01 to less than 10 parts by weight, e.g., 0.01 to 8 parts by weight, 0.01 to 5 parts by weight, 0.01 to 3 parts by weight, 0.01 to 1 part by weight, 0.01 to 1 part by weight, or 0.01 to 0.8 parts by weight, relative to 100 parts by weight of the total amount of the resin solids in the coating composition. The amount of the organic solvent may be 0.01 to 0.5 parts by weight, relative to 100 parts by weight of the total amount of the resin solids in the coating composition.

[0076] In one embodiment, the aqueous coating composition may include from 0.01 to 0.2 parts by weight of an organic solvent, for example, from 0.01 to 0.1 parts by weight. For example, the composition may be substantially free of organic solvent.

[0077] In the present invention, the total amount of the coating composition (100 parts by weight) can be defined as, for example, the total amount of the aqueous coating composition applied to the substrate film before the crystal orientation is completed (100 parts by weight).

[0078] In the present invention, by ensuring that the amount of organic solvent satisfies the above conditions, aggregation and gelation of the first and second silicone emulsions of the present invention can be suppressed, resulting in excellent coating uniformity, a reduction in the formation of coarse protrusions resulting from aggregates, and a well-balanced suppression of coating defects such as repelling.In addition, a release film exhibiting easy releasability can be obtained.

[0079] Furthermore, since the release layer can be sufficiently cured, the release layer has excellent solvent resistance. Furthermore, for example, the force required to peel the ceramic green sheet can be suppressed from increasing, which reduces damage to the ceramic green sheet during peeling and prevents defects.

[0080] Furthermore, according to the present invention, when an aqueous coating composition is applied onto a polyester film, the occurrence of coating defects such as repelling during the drying process can be suppressed, and coating defects such as uneven thickness of the release layer, the occurrence of coarse protrusions, and coating voids can be suppressed.

[0081] For example, in the present invention, in an embodiment in which a release film is produced using an in-line coating method, a release layer that is excellent in hardening and releasability can be formed, and the required physical properties can also be obtained with respect to the wettability of the ceramic slurry, which has previously been considered difficult.

[0082] In the present invention, the organic solvent includes a type 2 organic solvent (organic solvent) that is subject to the Organic Solvent Poisoning Prevention Regulations, such as acetone, isopropyl alcohol, ethyl ether, cellosolve, dichlorobenzene, xylene, cresol, ethyl acetate, methyl acetate, cyclohexanol, dioxane, dimethylformamide, toluene, normal hexane, butanol, methanol, and methyl ethyl ketone.

[0083] In the present invention, the phrase "substantially free of organic solvents" in a composition means that the organic solvent is contained in an amount of 0 to less than 0.01 parts by mass relative to 100 parts by mass of the total amount of the aqueous coating composition. This is because, even if an organic solvent is not actively added, organic solvents may be contained in contaminants derived from foreign matter, raw material resins, additives, etc.

[0084] (a) The first silicone emulsion having at least two or more alkenyl groups per molecule is an aqueous dispersion obtained by emulsifying a silicone containing at least two or more alkenyl groups per molecule. The silicone containing at least two or more alkenyl groups per molecule may be any compound having a siloxane bond in the main chain, but polyorganosiloxanes having alkenyl groups at the terminal and / or side chain are preferred, and polydimethylsiloxanes are more preferred. It is preferable that one molecule has 2 to 20 alkenyl groups. Having two or more alkenyl groups results in a release layer with a high crosslink density when thermally cured, exhibiting easy releasability.

[0085] Examples of silicones having an alkenyl group include those having a structure represented by the following general formula (I).

[0086]

[0087] (In general formula (I), R １ may be the same or different and are alkenyl groups having from 2 to 8 carbon atoms, or monovalent hydrocarbon groups having from 1 to 16 carbon atoms, including alkyl groups or aryl groups; R １ At least two of R are alkenyl groups having 2 to 8 carbon atoms. ２ may be the same or different, and are monovalent hydrocarbon groups containing 1 to 16 carbon atoms, including an alkyl group or an aryl group, and when a1 + b1 is 100 mol %, a1 is 90 mol % to 100 mol %, and b1 is 0 mol % to 10 mol %.) [SiO] ａ１ R bonded to a silicon atom represented by ２ is a monovalent hydrocarbon group containing an alkyl group or an aryl group, but is preferably a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from alkyl groups or aryl groups, more preferably a methyl group or a phenyl group, and even more preferably a methyl group. ２／２ It is preferable that the silicone is a silicone having a D unit structure represented by the following formula:

[0088] [SiO] ｂ１ R bonded to a silicon atom represented by １ is an alkenyl group having 2 to 8 carbon atoms, or a monovalent hydrocarbon group containing an alkyl group or an aryl group, ｂ１ R bonded to a silicon atom represented by １ Preferably, at least one of R is an alkenyl group having 2 to 8 carbon atoms. １ is preferably an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms selected from an alkyl group or an aryl group, more preferably a methyl group or a phenyl group, and even more preferably a methyl group.

[0089] R at both ends １ Also [SiO] ｂ１ R bonded to a silicon atom represented by １The preferred structure is an alkenyl group having 2 to 8 carbon atoms. A terminal alkenyl group is particularly preferred because it causes relatively little steric structural hindrance when reacted with a hydrogen group, making it easy to improve peelability.

[0090] R １ Examples of the alkenyl group having 2 to 8 carbon atoms represented by the formula (I) include a vinyl group, an allyl group, a butenyl group, a pentenyl group, and a hexenyl group, and among these, a vinyl group is particularly preferred.

[0091] [SiO] ａ１ and [SiO] ｂ１ When the total of the structural units is 100 mol %, from the viewpoint of localizing the hydrocarbon group on the surface of the release layer to improve the releasability, [SiO] ａ１ The range of the structural units is preferably 90 mol % or more and 100 mol % or less, and more preferably 92 mol % or more and 100 mol % or less.

[0092] The number average molecular weight of the silicone having an alkenyl group is preferably 1,000 or more but less than 50,000, more preferably 2,000 or more but less than 30,000. If the number average molecular weight is 1,000 or more, the hydrocarbon group is localized on the coating surface, making it easier to obtain sufficient releasability. On the other hand, if the number average molecular weight is less than 50,000, the emulsification properties into the aqueous coating composition tend to be good, and uniform application also tends to be good. The number average molecular weight in the present invention is １ H NMR and ２９ Siloxane units are identified from peaks observed in Si NMR, and the integral ratio is calculated from the integral ratio of the peaks derived from each siloxane unit.

[0093] (b) The second silicone emulsion having at least two or more hydrogen groups per molecule is an aqueous dispersion obtained by emulsifying a silicone having at least two or more hydrogen groups per molecule. As the silicone having at least two or more hydrogen groups per molecule, any compound having a siloxane bond in the main chain may be used, but polyorganosiloxane having a hydrogen group at the end or side chain is preferred, and polydimethylsiloxane is more preferred. The silicon atom at the end may have a hydrogen group, but preferably has a trialkylsilane structure such as trimethylsilane. It is preferable that there are 2 to 100 hydrogen groups per molecule. By having two or more hydrogen groups, a release layer with a high crosslink density is formed when cured, and it exhibits easy releasability.

[0094] Examples of silicones having a hydrogen group include those having a structure represented by the following general formula (II).

[0095]

[0096] (In general formula (II), R ３ may be the same or different and are monovalent hydrocarbon groups containing 1 to 16 carbon atoms, including an alkyl group or an aryl group, and when a2 + b2 is 100 mol %, a2 is 30 mol % to 90 mol % and b2 is 10 mol % to 70 mol %.

[0097] [SiO] ａ２ A hydrogen atom (hydrogen group) is bonded to the silicon atom represented by R ３ is a monovalent hydrocarbon group containing an alkyl group or an aryl group, but is preferably a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from alkyl groups or aryl groups. ２／２ It is preferable that the silicone is a silicone having a D unit structure represented by the following formula:

[0098] [SiO] ｂ２ , and R bonded to the terminal Si atom ３is a monovalent hydrocarbon group containing an alkyl group or an aryl group, and is preferably a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from alkyl groups or aryl groups.

[0099] Which R ３ Regarding the above, the number of carbon atoms in the alkyl group or aryl group is preferably smaller, since the steric structural hindrance is relatively small and the crosslinking reaction is facilitated. This is also preferable from the viewpoint of the fluidity of the coating liquid in the coating process and the uniformity of the reaction structure in the release layer. For this reason, the alkyl group is preferably a methyl group, an ethyl group, a propyl group, a butyl group, etc., and the aryl group is preferably a phenyl group, a tolyl group, etc.

[0100] [SiO] ａ２ and [SiO] ｂ２ When the total of the structural units is 100 mol%, [SiO] ａ２ The range of the structural unit is preferably 30 mol % or more and 90 mol % or less, and more preferably 40 mol % or more and 80 mol % or less. [SiO] ａ２ When the content of the structural unit [SiO] is 30 mol % or more, the number of crosslinking reaction points becomes sufficient, the crosslinking density of the release layer increases, and the abrasion resistance and solvent resistance of the release layer also become good, which is preferable. ａ２ When the structural unit is 90 mol % or less, hydrogen groups are less likely to remain in the release layer, the amount of uncrosslinked components in the release layer is less likely to increase, and the release properties are improved, which is preferable.

[0101] The number average molecular weight of the hydrogen group-containing silicone in the present invention is preferably 1,000 or more and 10,000 or less, more preferably 3,000 or more and 8,000 or less. When the number average molecular weight is 1,000 or more, sufficient releasability is easily obtained. On the other hand, when the number average molecular weight is 10,000 or less, the emulsification characteristics in the aqueous coating composition tend to be good and the coating uniformity also tends to be good. In addition, the crosslinking reaction tends to proceed efficiently, the remaining hydrogen groups in the release layer are reduced, and the releasability is good. The number average molecular weight in the present invention is １ H NMR and ２９Siloxane units are identified from peaks observed in Si NMR, and the integral ratio is calculated from the integral ratio of the peaks derived from each siloxane unit.

[0102] The content of the silicone contained in the (b) second silicone emulsion having a hydrogen group in the release layer is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 3 to 20 parts by mass, when the total amount of the silicone contained in the (a) first silicone emulsion having an alkenyl group, the silicone contained in the (b) second silicone emulsion having a hydrogen group, and the (c) substrate adhesion promoter described below is taken as 100 parts by mass. An amount of 1 part by mass or more is preferred because the crosslinking reaction proceeds sufficiently, making it easier to form a dense crosslinked structure and providing excellent releasability. An amount of 50 parts by mass or less is preferred because hydrogen groups are less likely to remain in the release layer, making it less likely that the activity of the release layer surface will increase, and good releasability will be maintained.

[0103] In one embodiment, the content of silicone contained in (b) the second silicone emulsion having a hydrogen group contained in the composition is less than the content of silicone contained in (a) the first silicone emulsion having an alkenyl group.

[0104] The content of the (a) first silicone emulsion is preferably 3 to 40 times the content of the (b) second silicone emulsion, and more preferably 5 to 30 times. By setting the content within this range, the crosslinking reaction between the vinyl groups and the hydrogen groups proceeds efficiently, resulting in a release layer with excellent releasability, which is preferable.

[0105] The (c) substrate adhesion promoter is not particularly limited, but is preferably one having a structure containing a hydrolyzable group bonded to a silicon atom directly or via another functional group and various organic functional groups, and more preferably a water-soluble or water-dispersible organic silane coupling agent.

[0106] Examples of the substrate adhesion promoter include compounds represented by the following formula (III): YSiX ３　...(III) Here, Y is a group having a functional group such as a vinyl group, an epoxy group, an isocyanurate group, a mercapto group, an amino group, a methacryl group, a styryl group, an acrylic group, an isocyanate group, an acid anhydride, or a carboxyl group, and it is particularly preferable that Y is an epoxy group, a vinyl group, or a carboxyl group. The functional group possessed by Y may be directly bonded to the Si element, or may be bonded via, for example, an alkyl group, an ether group, or an oxyalkylene group having 1 to 10 carbon atoms.

[0107] X is an alkylene group such as methylene, ethylene, or propylene, an alkyl group, or a hydrolyzable group such as methoxy, ethoxy, or acetoxy, and at least one of the three Xs is a hydrolyzable group, preferably all three Xs are hydrolyzable groups. The hydrolyzable group is preferably an ethoxy group or an acetoxy group.

[0108] Preferred substrate adhesion promoters include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, and vinylmethyldimethoxysilane.

[0109] Two or more types of substrate adhesion promoters may be used. When two or more types of water-soluble or water-dispersible organic silane coupling agents are used in combination, it is preferable that they at least have a structure containing a vinyl group in Y in formula (III), and a combination of a silane coupling agent in which an epoxy group is incorporated in Y and a silane coupling agent in which a vinyl group is incorporated in Y is more preferred. Having a structure in which Y has a vinyl group allows the release layer to react with the silane coupling agent, which is preferable because it provides excellent substrate adhesion, particularly immediate adhesion to the substrate. By using a silane coupling agent in which an epoxy group is incorporated in Y and a silane coupling agent in which a vinyl group is incorporated in Y in combination, for example, the silane coupling agent containing an epoxy group adheres to the substrate side, and the silane coupling agent containing a vinyl group forms a crosslinking reaction with the release layer, which is preferable because it provides excellent immediate adhesion to the substrate.

[0110] The content of the substrate adhesion imparting agent is preferably 0.1 parts by mass or more and 15 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less, and most preferably 3 parts by mass or more and 8 parts by mass or less, when the total mass of the total solid contents of (a), (b), and (c) is taken as 100 parts by mass. If the content of the substrate adhesion imparting agent is 0.1 parts by mass or more and 15 parts by mass or less, the substrate adhesion of the release layer, particularly immediate adhesion to the substrate, is improved. Furthermore, when a silane coupling agent is used as the substrate adhesion imparting agent, a crosslinking reaction proceeds due to a dehydration condensation reaction between the silane coupling agents, which increases the coating strength of the release layer and results in a release layer with excellent releasability.

[0111] The aqueous coating composition of the present invention preferably contains at least (d) a surfactant. The inclusion of a surfactant provides excellent coatability when the coating composition is applied to a polyester film substrate, and is therefore preferred because it prevents coating defects such as repelling. Furthermore, the stability of the emulsion present in the coating composition is not impaired, and there is no risk of aggregates or gelled products of the coating composition being mixed into the release layer, which is preferred because it prevents the occurrence of unevenness in the release layer and coating irregularities.

[0112] The surfactant is not particularly limited as long as it can solve the problems of the present invention and exhibit the desired effects. It is preferable to use a material that can reduce the amount of volatilization of the surfactant during the heating process for stretching and crystallizing the substrate film and that remains in the release layer. The surfactant remaining in the release layer is preferable because it enhances the wettability of the release layer to ceramic slurries that use organic solvents.

[0113] Although not limited to a specific theory, the surfactant according to the present invention has a high boiling point and a specific structure, so that it can remain in the release layer and achieve both wettability and releasability. On the other hand, if the surfactant according to the present invention remains in the release layer, it is desirable to improve immediate adhesion after processing the release layer. In response to this requirement, the present invention has also succeeded in improving immediate adhesion after processing the release layer by including a substrate adhesion promoter.

[0114] As the surfactant, cationic, anionic, and nonionic surfactants can be suitably used, but nonionic surfactants are preferred from the viewpoint of enhancing emulsion stability. Examples include at least one selected from alkylene oxide adducts such as alkylene oxide adducts of higher alcohols or higher fatty acids, esters of alkylene oxide adducts of higher fatty acids and alcohols, alkylene oxide adducts of alkanolamides, alkylene oxide adducts of sorbitan esters, and alkylene oxide adducts of higher fatty acid glycerides. The surfactant used preferably has an HLB value in the range of 6 to 18. The HLB value is a value calculated using Griffin's formula.

[0115] Examples of alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide, and these may be used alone or in combination. When using multiple alkylene oxides, either block or random addition may be used, but the HLB value is preferably in the range of 8 to 18, and more preferably in the range of 10 to 15. Among these nonionic emulsifiers, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, and the like are preferred. If a nonionic emulsifier with an HLB value outside this range is used as an emulsifier for a silicone aqueous dispersion, the emulsifying and dispersing power and the stability of the aqueous dispersion may be reduced.

[0116] Examples of the alkylene oxide used in the present invention include the structure shown in the following formula (IV).

[0117] H ２ｍ＋１ C ｍ -O-(CH ２ -CH ２ -O) ｎ —H (IV) (In formula IV, m and n are integers of 1 to 30. The number m represents the alkyl group chain length, and the number n represents the number of moles of ethylene oxide added.)

[0118] The larger the number of m and the longer the alkyl group chain length, the better the lipophilicity and the better the stability of the aqueous silicone emulsion, which is preferable. Also, the larger the number of n and the number of ethylene oxides, the better the hydrophilicity and the higher the stability of the aqueous silicone emulsion, which is preferable. The numbers of m and n can take any value in the range of 1 to 30, but the larger the number, the higher the molecular weight, and the more the surfactant remains in the release layer without volatilizing during the heat curing process of the coating composition and the stretching and crystallization process of the substrate film, which is preferable because it results in a release film with excellent wettability.

[0119] In order to allow the surfactant to remain in the release layer, the number average molecular weight of the surfactant is 400 or more, and the number average molecular weight of the surfactant is preferably in the range of 400 to 2000, more preferably in the range of 400 to 1000, and even more preferably in the range of 450 to 1000.

[0120] A number-average molecular weight of 400 or more is preferable because the surfactant remains in the release layer without volatilizing during the heat-curing process of the coating composition and the stretching and crystallization process of the substrate film, resulting in a release film with excellent wettability. A number-average molecular weight of 2000 or less is less likely to deteriorate the stability of the emulsion or the coatability of the coating composition. In addition, the surfactant segregates on the surface of the release layer during the heat-curing process of the release layer, thereby improving wettability.

[0121] The boiling point of the surfactant is preferably 200° C. or higher, more preferably 210° C. or higher, also preferably 230° C. or higher, and may be 250° C. or higher. If the boiling point of the surfactant is 200° C. or higher, the surfactant remains in the release layer without volatilizing during the heat curing step of the coating composition and the stretching and crystallization step of the substrate film, which is preferable because the release layer has excellent wettability.

[0122] For example, the boiling point of the surfactant is from 200° C. to 350° C., and may be from 200° C. to 320° C. When the boiling point of the surfactant is within the above range, the surfactant can be prevented from rapidly volatilizing during the process of drying and solidifying the release layer, and deterioration of wettability can be prevented.

[0123] In the present invention, since the number average molecular weight of the surfactant is 400 or more, the surfactant may be semi-solid or solid at room temperature. Preferably, the surfactant has a boiling point within the above range. When the surfactant has a boiling point, the aqueous coating composition can be prepared and applied more easily than when the surfactant is solid at room temperature, and a release film with excellent wettability can be obtained.

[0124] The content of the surfactant (d) contained in the coating composition is preferably 0.1 to 20 parts by mass, more preferably 1 to 15 parts by mass, even more preferably 3 to 15 parts by mass, and most preferably 5 to 15 parts by mass, when the total mass of all solids of (a), (b), and (c) is taken as 100 parts by mass. An amount of 0.1 parts by mass or more is preferred because it provides excellent coatability when applied to a polyester film, and the surfactant remains in the release layer, resulting in excellent wettability. An amount of 20 parts by mass or less is preferred because there is no risk of excessive residual surfactant causing heavy release.

[0125] In the present invention, the surface tension of the aqueous coating composition is preferably 10 to 40 mN / m, and more preferably 10 to 35 mN / m. A surface tension of 10 mN / m or more is preferred because it levels when applied to a substrate film, resulting in a uniform coating appearance without streaks or the like. A surface tension of 40 mN / m or less is preferred because the aqueous coating composition easily wets and spreads on the substrate film, improving emulsion stability. Furthermore, this is preferred because the amount of surfactant contained in the aqueous coating composition is sufficient, and the surfactant remaining in the release layer after heat curing can enhance the wettability of ceramic slurries and the like.

[0126] (Platinum-Based Catalyst) The aqueous coating composition of the present invention requires the use of a platinum-based catalyst to cause an addition reaction between a silicone having an alkenyl group and a silicone having a hydrogen group. Known platinum-based catalysts can be used, such as platinum chloride and chloroplatinic acid. In consideration of dispersibility in silicone, the platinum-based catalyst may be a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt's catalyst), which can be dispersed simultaneously with the emulsification of silicone to ensure uniform dispersion.

[0127] The amount of platinum catalyst is preferably in the range of 10 to 800 ppm by mass of platinum element relative to the total amount of (a) the silicone contained in the first silicone emulsion having an alkenyl group and (b) the silicone contained in the second silicone emulsion having a hydrogen group, which form the release layer. By setting the amount in this range, the silicone can be sufficiently cured and the generation of aggregates can be suppressed, resulting in a release film with excellent smoothness. A mass ratio of platinum element of 800 ppm or less is preferable because it accelerates the addition reaction between the alkenyl group and the hydrogen group, preventing the risk of silicone aggregates being generated. The amount of platinum catalyst is more preferably 600 ppm or less, even more preferably 500 ppm or less, and even more preferably 300 ppm or less. Furthermore, an amount of 10 ppm or more is preferable because the silicone addition reaction proceeds efficiently, resulting in sufficient curing of the release layer and exhibiting light releasability.

[0128] (Reaction Inhibitor) The aqueous coating composition of the present invention preferably contains a reaction inhibitor to suppress the activity of the platinum-based catalyst at room temperature. The content of the reaction inhibitor is preferably 5 to 1000 ppm, more preferably 10 to 700 ppm, and more preferably 20 to 500 ppm, relative to the total mass of the aqueous coating composition. A content of 5 ppm or more is preferable because the effect of suppressing the activity of the platinum-based catalyst is sufficient. A content of 1000 ppm or less is preferable because there is no risk of the reaction inhibitor volatilizing during heat treatment contaminating the inside of the oven.

[0129] The aqueous coating composition of the present invention may further contain colorants, ultraviolet absorbers, particles, etc., within the scope of not impairing the object of the present invention.

[0130] (Other Features of the Release Layer) The film thickness of the release layer in the present invention is preferably 0.001 to 0.2 μm, and more preferably 0.005 to 0.1 μm, as the thickness after drying. A thickness of 0.001 μm or more is preferred because a release layer with excellent releasability can be obtained. A thickness of 0.2 μm or less is preferred because it is not necessary to increase the solids concentration of the release layer components of the aqueous coating composition or the coating amount, and excellent coatability can be obtained when applying the composition to a substrate film.

[0131] (Method for producing a release film) In one embodiment, a release layer is formed on at least one surface of a substrate film. The release layer is formed by applying an aqueous coating composition to the substrate film, followed by heat drying, and then reacting and solidifying the components in the aqueous coating composition. The release layer is preferably formed during the film formation process.

[0132] When applying an aqueous coating composition to a substrate film, the solids concentration is preferably 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less, based on the components in the aqueous coating composition, i.e., the solids. When the solids concentration of the release layer components in the aqueous coating composition is above the lower limit, the film-forming properties tend to be good. When the solids concentration is below the upper limit, the stability of the aqueous coating composition and the appearance of the release layer tend to be good. Water is preferably used as the aqueous solvent for adjusting the solids concentration.

[0133] The aqueous coating composition to be applied to the substrate film to form the release layer can be applied at any stage, but is preferably applied during the polyester film manufacturing process, and more preferably to the polyester film before the completion of orientation crystallization. Thereafter, the polyester film is stretched in at least one direction and then heat-treated to complete the crystal orientation.

[0134] Here, polyester films before the completion of crystal orientation include unstretched films, uniaxially oriented films obtained by orienting unstretched films in either the longitudinal direction (hereinafter sometimes referred to as the direction of continuous film production, longitudinal direction, or MD direction) or the transverse direction (hereinafter sometimes referred to as the direction perpendicular to the longitudinal direction, width direction, or TD direction), and also films that have been stretched and oriented at a low ratio in both the longitudinal and transverse directions (biaxially stretched films before they are finally re-stretched in the longitudinal or transverse direction to complete the orientation crystallization).

[0135] Among these, so-called in-line coating is preferred, in which an aqueous coating composition is applied to an unstretched film or a uniaxially stretched film oriented in one direction, followed by longitudinal stretching and / or transverse stretching and heat setting. The release layer may be dried by a stretching step or heat setting treatment after application, and a drying step may be added as needed. In addition, when the composition is cured using a catalyst to obtain a cured coating, the composition can be cured by a stretching step or heat setting treatment, but a curing step may be added as needed.

[0136] For example, in a drying step in which an aqueous coating composition is applied to one surface of a polyester film and then the coated film is dried, the drying temperature may be 60°C or higher and 140°C or lower, for example, 60°C or higher and 130°C or lower, or 60°C or higher and 120°C or lower.

[0137] A temperature of 60° C. or higher is preferred because the composition is not dried sufficiently, which can prevent breakage of the film when the polyester film is stretched in the stretching step.A temperature of 140° C. or lower can prevent rapid drying of the composition and suppress aggregation and gelation of the emulsion, resulting in excellent coating uniformity, a reduction in coarse protrusions resulting from aggregates, and a balanced suppression of coating defects such as repelling.

[0138] Furthermore, the present invention can significantly reduce the amount of organic solvent used in coating compositions containing organic solvents as a main component, or can even eliminate the use of organic solvents, thereby significantly reducing the adverse effects on the human body caused by contact with organic solvents or inhalation of their vapors, and the burden on the global environment caused by the release of organic solvent vapors into the atmosphere.

[0139] Furthermore, there is no need to use explosion-proof equipment for drying organic solvents, and energy consumption during operation can be reduced compared to conventional manufacturing equipment. ２ It also reduces emissions and reduces the burden on the environment.

[0140] By providing a stretching step after a drying step of drying the applied aqueous coating composition, the film temperature in the stretching step of the polyester film becomes sufficient, and there is no risk of breakage or uneven thickness of the release film in the stretching step, which is preferable. In the stretching step, after drying the water in the aqueous coating composition, the polyester film as the substrate is preferably heated to a temperature equal to or higher than the glass transition temperature, and the stretching temperature in the stretching step is, for example, 60°C or higher and 160°C or lower, preferably 60°C or higher and 150°C or lower, and preferably 70°C or higher and 150°C or lower, from the viewpoint of stretchability.

[0141] In one embodiment, the stretching step is carried out at a higher temperature than the drying step.

[0142] In the manufacturing method of the present invention, it is preferable to have a heat setting step in which the stretched polyester film is heat-treated to complete crystal orientation in order to impart dimensional stability and mechanical properties to the release film. The temperature of the heat setting step is preferably as high as possible to promote crystallization of the polyester film and hardening of the release layer, but is preferably a temperature below the melting point of the polyester. Specifically, it is preferably 180°C or higher and 250°C or lower, and more preferably 200°C or higher and 240°C or lower. A temperature of 180°C or higher is preferable because the hardening of the release layer progresses sufficiently and the dimensional stability and mechanical properties of the polyester film are sufficient. A temperature of 250°C or lower is preferable because the crystals of the polyester film do not melt, and a release film with excellent flatness can be obtained.

[0143] In the present invention, the aqueous coating composition contains a certain amount of a substrate adhesion promoter. When a silane coupling agent is used as the substrate adhesion promoter, it is preferable to apply a temperature of 180°C or higher, more preferably 200°C or higher, to promote dehydration condensation between the silane coupling agents. Curing the release layer at a temperature of 180°C or higher is preferable because it facilitates the reaction between the silane coupling agents and results in a release layer with a high crosslink density. In the case of offline coating, in which a release layer is formed by applying the coating to one side of a substrate film, such as a biaxially oriented polyester film, and then heat-treating it, applying a temperature of 180°C or higher can cause thermal deformation or shrinkage of the substrate film, potentially resulting in a deterioration in the flatness of the release film. When the release layer is cured at a temperature of 180°C or lower, the dehydration condensation reaction of the silane coupling agent is insufficient, which can result in a decrease in substrate adhesion and heavy release due to a decrease in crosslink density. Therefore, in the present invention, it is preferable to form the release layer by inline coating.

[0144] Regarding the release layer in the present invention, the specifications that "an aqueous coating composition is applied to an unstretched film or a uniaxially stretched film oriented in one direction, and the film is then stretched longitudinally and / or transversely and heat-set" and "the release layer is formed by an in-line coating method" specify the structure of the product by the manufacturing method, but there are circumstances in which it is impossible or almost impractical to directly identify the product by its structure or properties, as follows.

[0145] In the present invention, the aqueous coating composition that forms the release layer is stretched longitudinally and / or transversely together with the film to which it is applied, and it is presumed that this causes (a) the silicone contained in the first silicone emulsion, (b) the silicone contained in the second silicone emulsion, (c) the substrate adhesion promoter, and (d) the surfactant to become oriented and interact with each other.

[0146] For example, it is thought that during the process of drying water in the aqueous coating composition, during stretching of the substrate film, or during curing of the release layer, differences in compatibility and molecular weight among (a) the silicone contained in the first silicone emulsion, (b) the silicone contained in the second silicone emulsion, (c) the substrate adhesion promoter, and (d) the surfactant make (c) the substrate adhesion promoter more likely to localize at the interface with the substrate, thereby improving substrate adhesion.

[0147] However, it is difficult to structurally specify the orientation and distribution of the resin components in the release layer, and the distribution of substituents that contribute to releasability on the surface of the release layer.

[0148] Furthermore, even in light of the measurement technology available at the time of filing the present invention, it is impossible or impractical to measure the structure or characteristics of the release film of the present invention and to analyze and identify its physical properties based on these results. Therefore, at the time of filing the present invention, there are circumstances in which it is impossible or impractical to directly identify the product by its structure or characteristics.

[0149] The aqueous coating composition can be applied by any known coating method, such as roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, curtain coating, or the like, which can be used alone or in combination.

[0150] In one aspect, the manufacturing method of the present invention provides a method for manufacturing a release film for manufacturing a resin sheet and a multilayer ceramic capacitor.

[0151] (Resin Sheet) The resin sheet of the present invention is not particularly limited as long as it is a sheet molded on the surface of the release layer opposite the substrate. Examples include a resin sheet obtained by curing a resin sheet molding composition containing a resin component and a crosslinking agent, and a resin sheet molded by melt casting or solution casting using an organic component having film-forming properties. In one embodiment, the release film of the present invention is a release film for molding a resin sheet containing an inorganic compound. Examples of inorganic compounds include metal particles, metal oxides, and minerals, such as calcium carbonate, silica particles, aluminum particles, and barium titanate particles. Because the present invention has a highly smooth release layer, even in embodiments in which the resin sheet contains these inorganic compounds, defects that can be attributed to inorganic compounds, such as breakage of the resin sheet and difficulty in peeling the resin sheet from the release layer, can be suppressed.

[0152] The resin component forming the resin sheet can be appropriately selected depending on the application. In one embodiment, the resin sheet containing an inorganic compound is a ceramic green sheet. For example, the ceramic green sheet can contain barium titanate as the inorganic compound. Furthermore, the resin component can contain, for example, a polyvinyl butyral resin.

[0153] (Ceramic Green Sheet and Ceramic Capacitor) Generally, a multilayer ceramic capacitor has a rectangular parallelepiped ceramic body. First internal electrodes and second internal electrodes are alternately provided inside the ceramic body along the thickness direction. The first internal electrodes are exposed at a first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrode is electrically connected to the first external electrode at the first end face. The second internal electrode is exposed at a second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrode is electrically connected to the second external electrode at the second end face.

[0154] In one embodiment, the release film of the present invention is a release film for producing a ceramic green sheet, and is used to produce such a multilayer ceramic capacitor.

[0155] For example, when the release film for producing ceramic green sheets of the present invention is used, ceramic green sheets are produced, for example, as follows. First, using the release film of the present invention as a carrier film, a ceramic slurry for forming a ceramic body is applied and dried. A conductive layer for forming a first or second internal electrode is printed on the applied and dried ceramic green sheet. A ceramic green sheet, a ceramic green sheet on which a conductive layer for forming a first internal electrode is printed, and a ceramic green sheet on which a conductive layer for forming a second internal electrode is printed are appropriately laminated and pressed to obtain a mother laminate. The mother laminate is divided into multiple pieces to produce green ceramic bodies. The green ceramic bodies are fired to obtain ceramic bodies. Then, first and second external electrodes are formed to complete a multilayer ceramic capacitor.

[0156] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. The property values ​​used in the present invention were evaluated using the following methods.

[0157] (Release Layer Thickness) After cutting the release film into triangular pieces, a 2 nm thick Pt (platinum) layer was formed on the release layer surface by coating. The obtained sample was fixed in a multi-axis embedding capsule, embedded using epoxy resin, and sliced ​​perpendicular to the film surface using a microtome ULTRACUT-S to obtain an ultrathin sample with a thickness of 50 nm. The obtained ultrathin sample was then mounted on a grid and steam-stained with 2% osmic acid at 60 °C for 2 hours. Using the ultrathin sample after steam staining, the film cross section was observed using a transmission electron microscope LEM-2000 at an acceleration voltage of 100 kV, and the thickness of the release layer was measured. Measurements were performed at 10 random points, and the average value was taken as the thickness of the release layer.

[0158] (Surface tension) The surface tension of the aqueous coating composition was measured by the pendant drop method using a contact angle meter (Kyowa Interface Science Co., Ltd., fully automatic contact angle meter DM-701) under conditions of 23°C and 50% RH. After forming the maximum amount of liquid drop that could be held without dropping, the surface tension was calculated by the ds / de method using the attached analysis software FAMAS. The measurement was performed five times in total, and the average value was used.

[0159] (Coating Uniformity of Release Layer) A release film roll prepared by the method described in the following examples was unwound within 30 minutes of completion of winding, and an A4 cut sample was collected and evaluated. The release layer surface was visually observed using a fluorescent lamp and a halogen light, and the number of aggregated coating defects (number per A4 sheet) was compared and evaluated according to the following criteria: ◯: No coating defects △: 1 to 10 coating defects ×: 10 or more coating defects

[0160] (Immediate Adhesion to Substrate) A release film roll prepared by the method described in the following examples was unwound and collected within 30 minutes of completion of winding, and an evaluation was performed on an A4 cut sample. The release surface of the release film was rubbed 10 times with a thumb at a load of approximately 500 gf, and a writing test was performed with a magic marker (manufactured by Teranishi Chemical Industry Co., Ltd., extra thick, MGD-T2) to check for silicone detachment from the rubbed area. Evaluation was performed according to the degree of writing with the magic marker, using the following criteria: ⊚: No difference between the non-rubbed area and the rubbed area, with magic marker repellency observed in both. ◯: There was a difference between the non-rubbed area and the rubbed area, with magic marker repellency observed in both. △: Magic marker repellency observed in part of the rubbed area, with the majority being wet with magic marker. ×: The entire rubbed area was wet with magic marker, and no repellency was observed.

[0161] (Releasability of ceramic green sheet) A slurry composition I consisting of the following materials was mixed by stirring for 10 minutes and dispersed with zirconia beads having a diameter of 0.5 mm using a bead mill for 10 minutes to obtain a primary dispersion. Then, a slurry composition II consisting of the following materials was added to the primary dispersion so that the ratio of (slurry composition I):(slurry composition II) was 3.4:1.0, and a secondary dispersion was performed with zirconia beads having a diameter of 0.5 mm using a bead mill for 10 minutes to obtain a ceramic slurry. (Slurry composition I) Toluene 22.3 parts by mass Ethanol 18.3 parts by mass Barium titanate (average particle size 100 nm) 57.5 parts by mass Homogenol L-18 (Kao Corporation) 1.9 parts by mass (Slurry composition II) Toluene 39.6 parts by mass Ethanol 39.6 parts by mass Dioctyl phthalate 3.3 parts by mass Polyvinyl butyral (S-LEC BM-S, Sekisui Chemical Co., Ltd.) 16.3 parts by mass 1-ethyl-3-methylimidazolium ethyl sulfate 0.5 parts by mass

[0162] Next, a release film roll prepared by the method described in the Examples below was unwound within 30 minutes of completion of winding, and an A4-sized sample was taken. The release surface of the sample was coated with an applicator so that the slurry would be 1.0 μm thick after drying, and the sample was dried at 60°C for 1 minute to obtain a release film with a ceramic green sheet. The resulting release film with a ceramic green sheet was then de-ionized using a static eliminator (Keyence Corporation, SJ-F020), and then peeled using a peel tester (Kyowa Interface Science Co., Ltd., VPA-3, load cell load 0.1 N) at a peel angle of 90°, a peel temperature of 25°C, and a peel rate of 0.3 m / min. For the peeling direction, 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 the double-sided tape by adhering the ceramic green sheet side to the tape, and the release film side was pulled to peel it off. Of the obtained measured values, the average value of the peel force for peel distances of 20 mm to 70 mm was calculated and this value was taken as the peel force. Measurements were carried out a total of five times, and the average value of the peel forces was used for evaluation. The obtained peel force values ​​were judged according to the following criteria: ◯: Less than 1.0 mN / mm △: Less than 3.0 mN / mm ×: 3.0 mN / mm or more

[0163] (Appearance of Slurry Application) A ceramic slurry prepared in the same manner as in the evaluation of the releasability of the ceramic slurry was diluted two-fold with toluene, and a ceramic green sheet having a thickness of 1.0 μm was molded on the release surface of a release film. The edge surface of the ceramic green sheet molded on the release film was observed from the surface on which the ceramic green sheet was laminated, and visually evaluated according to the following criteria: ○: The edge surface and the entire surface of the ceramic green sheet were uniform to the naked eye. △: The edge surface and the entire surface of the ceramic green sheet were uniform to the naked eye, and the edge surface was uneven when viewed with an optical microscope. ×: The edge surface or the entire surface of the ceramic green sheet was uneven to the naked eye.

[0164] (Silicone emulsion: a-1) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Labs, device name "Ultra Planetary Mixer"), a silicone emulsion containing 99 mol % of a1 in formula (I), 1 mol % of b1, and R １ and [SiO] ａ１R bonded to a silicon atom represented by ２ is a methyl group, and [SiO] ｂ１ R bonded to a silicon atom represented by １ One of them is a methyl group, and the other is R １ A silicone emulsion a-1 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil having a number average molecular weight of 27,000, in which each of the groups is a vinyl group, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 582, boiling point 283°C) surfactant having 12 alkyl chains and 9 ethylene oxide chains (structure represented by formula (IV) where n = 9, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification. ２ｍ＋１ C ｍ -O-(CH ２ -CH ２ -O) ｎ -H (IV)

[0165] (Silicone emulsion: a-2) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), a silicone emulsion containing 99 mol % of a1 in formula (I), 1 mol % of b1, and R １ and [SiO] ａ１ R bonded to a silicon atom represented by ２ is a methyl group, and [SiO] ｂ１ R bonded to a silicon atom represented by １ One of them is a methyl group, and the other is R １ A silicone emulsion a-2 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 95% by mass of silicone oil having a number average molecular weight of 27,000 and in which each of the groups is a vinyl group, and 5.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 582, boiling point 283°C) surfactant having 12 alkyl chains and 9 ethylene oxide chains (structure represented by formula (IV) where n = 9, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification.

[0166] (Silicone emulsion: a-3) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Labs, device name "Ultra Planetary Mixer"), a silicone emulsion containing 99 mol % of a1 in formula (I), 1 mol % of b1, and R １ and [SiO] ａ１ R bonded to a silicon atom represented by ２ is a methyl group, and [SiO] ｂ１ R bonded to a silicon atom represented by １ One of them is a methyl group, and the other is R １ A silicone emulsion a-3 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil having a number average molecular weight of 27,000 and in which each of the groups is a vinyl group, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 450, boiling point 230°C) surfactant having 12 alkyl chains and 6 ethylene oxide chains (structure represented by formula (IV) where n = 6, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification.

[0167] (Silicone emulsion: a-4) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Labs, device name "Ultra Planetary Mixer"), a silicone emulsion containing 99 mol % of a1 in formula (I), 1 mol % of b1, and R １ and [SiO] ａ１ R bonded to a silicon atom represented by ２ is a methyl group, and [SiO] ｂ１ R bonded to a silicon atom represented by １ One of them is a methyl group, and the other is R １ A silicone emulsion a-4 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil having a number average molecular weight of 27,000 and in which each of the groups is a vinyl group, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 446, boiling point 214°C) surfactant having 18 alkyl chains and 4 ethylene oxide chains (structure represented by formula (IV) where n = 4, m = 18) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification.

[0168] (Silicone emulsion: a-5) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Labs, device name "Ultra Planetary Mixer"), a silicone emulsion containing 99 mol % of a1 in formula (I), 1 mol % of b1, and R １ and [SiO] ａ１ R bonded to a silicon atom represented by ２ is a methyl group, and [SiO] ｂ１ R bonded to a silicon atom represented by １ One of them is a methyl group, and the other is R １ A silicone emulsion a-5 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil having a number average molecular weight of 27,000 and in which each of the groups is a vinyl group, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 362, boiling point 182°C) surfactant having 12 alkyl chains and 4 ethylene oxide chains (structure represented by formula (IV) where n = 4, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification.

[0169] (Silicone emulsion: b-1) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), a silicone emulsion containing 50 mol % of a2 and 50 mol % of b2 in formula (II) and R ３ A silicone emulsion b-1 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil in which all of the groups are methyl groups and the number average molecular weight is 5,500, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 582, boiling point 283°C) surfactant having 12 alkyl chains and 9 ethylene oxide chains (structure represented by formula (IV) where n = 9, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0170] (Silicone emulsion: b-2) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), a silicone emulsion containing 50 mol % of a2 and 50 mol % of b2 in formula (II) and R ３ A silicone emulsion b-2 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil in which all of the groups are methyl groups and the number average molecular weight is 5,500, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 450, boiling point 230°C) surfactant having 12 alkyl chains and 6 ethylene oxide chains (structure represented by formula (IV) where n = 6, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0171] (Silicone emulsion: b-3) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), a silicone emulsion containing 50 mol % of a2 and 50 mol % of b2 in formula (II) and R ３ A silicone emulsion b-3 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil in which all of the groups are methyl groups and the number average molecular weight is 5,500, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 446, boiling point 214°C) surfactant having 18 alkyl chains and 4 ethylene oxide chains (structure represented by formula (IV) where n = 4, m = 18) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0172] (Silicone emulsion: b-4) Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), a silicone emulsion containing 50 mol % of a2 and 50 mol % of b2 in formula (II) and R ３A silicone emulsion b-4 having a solids content of 40% by mass was obtained by mechanically emulsifying raw materials consisting of 91% by mass of silicone oil in which all of the groups are methyl groups and the number average molecular weight is 5,500, and 9.0% by mass of a polyoxyethylene alkyl ether (number average molecular weight 362, boiling point 182°C) surfactant having 12 alkyl chains and 4 ethylene oxide chains (structure represented by formula (IV) where n = 4, m = 12) in an aqueous medium. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0173] (Substrate Adhesion Promoting Agent: c-1) A mixture of 3-glycidyloxypropyltrimethoxysilane and triacetoxyvinylsilane in a mass ratio of 1:1 was used.

[0174] (Substrate adhesion promoter: c-2) Triacetoxyvinylsilane was used.

[0175] Aqueous Coating Composition Production Example 1 Silicone emulsion (a-1), silicone emulsion (b-1), substrate adhesion promoter (c-1), and water were mixed in the proportions shown in Table 1 to obtain an aqueous coating composition with a solids concentration of 4% by mass. The surfactant contained in silicone emulsions (a-1) and (b-1) was a polyoxyethylene alkyl ether having 12 alkyl chains and 4 ethylene oxide chains (the structure shown in formula (IV) where n = 4 and m = 12), and the surfactant content was 8.6% by mass. Furthermore, 0.02% by mass of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: CAT-PM-10A) and 150 ppm of a crosslinking reaction inhibitor (1-ethynylcyclohexanol) were mixed in the aqueous coating composition.

[0176] <Aqueous Coating Composition Production Examples 2 to 12> Aqueous coating compositions were obtained in the same manner as in Production Example 1, except that the ingredients were mixed so as to satisfy the types and ratios shown in Table 1.

[0177] Example 1 Polyethylene terephthalate ([η] = 0.63 dl / g, Tg = 78°C) containing 0.25% by mass of calcium carbonate particles with an average particle size of 0.6 μm was melted in an extruder, passed through a filter with a filtration accuracy of 10 μm, extruded from a die, and cooled on a cooling drum in a conventional manner to form an unstretched film. The polyester film was then stretched 3.2 times in the longitudinal direction at 80°C, and the aqueous coating composition obtained in Production Example 1 was uniformly applied to one surface of the polyester film using a roll coater. This coated film was then dried at 115°C, stretched 4.0 times in the transverse direction at 145°C, and further heat-set at 230°C for approximately 10 seconds, followed by winding up into a roll to obtain a roll of release film (thickness 25 μm) having a release layer as shown in Table 1. The release film was unwound from the resulting release film roll and cut into an A4 size sample, and the evaluations described in Table 1 were performed using the samples. The amount of the aqueous coating composition applied was such that the thickness of the release layer after stretching was as shown in Table 1.

[0178] Examples 2 to 10 and Comparative Examples 1 and 2 Release films were obtained in the same manner as in Example 1, except that the aqueous coating compositions obtained in the production examples shown in Table 1 were used.

[0179] Comparative Example 3 A release film was obtained in the same manner as in Example 1, except that the aqueous coating composition described in Production Example 1 was prepared so that it contained 20 mass % of isopropyl alcohol as an organic solvent based on the total amount of the aqueous coating composition.

[0180] As shown in Table 1, in Examples 1 to 10, release films were obtained that were excellent in the coating uniformity of the release layer, immediate adhesion to the substrate, slurry coating appearance, and releasability.

[0181] In contrast, in Comparative Example 1, the release layer was formed using an aqueous coating composition that did not contain a substrate adhesion promoter, resulting in poor immediate adhesion to the substrate. The release layer was transferred to the roll during the release film manufacturing process and to the back of the release film when the release film roll was wound up, resulting in defects in the release layer and poor releasability. In Comparative Example 2, a silicone emulsion was used that used a surfactant with a low number-average molecular weight and a low boiling point, which caused the surfactant to volatilize during the drying and solidification process of the aqueous coating composition, resulting in poor slurry coating appearance. In Comparative Example 3, an aqueous coating composition containing isopropyl alcohol as the organic solvent was used, resulting in unstable emulsions, which led to poor release surface smoothness due to aggregates and cissing defects. As a result, the coating uniformity of the release layer was poor. Furthermore, the release layer was insufficiently cured, resulting in poor immediate adhesion to the substrate, poor slurry appearance, and poor releasability.

[0182]

[0183] The release film of the present invention has high peelability and wettability of the release layer and excellent immediate adhesion to the substrate, so that the occurrence of defects can be suppressed when forming a thin resin sheet, particularly a ceramic green sheet.

Claims

1. A release film having a release layer on at least one side of a polyester film, wherein the release layer is a layer formed by reacting and solidifying an aqueous coating composition, wherein the aqueous coating composition contains 10 parts by mass or less of an organic solvent per 100 parts by mass of the total amount of the aqueous coating composition, and the aqueous coating composition contains: (a) a first silicone emulsion containing at least two alkenyl groups per molecule; (b) a second silicone emulsion containing at least two hydrogen groups per molecule; (c) a substrate adhesion promoter; and (d) a surfactant having a number average molecular weight of 400 or more.

2. The release film according to claim 1, wherein the (c) substrate adhesion promoter is a water-soluble or water-dispersible silane coupling agent having a hydrolyzable functional group bonded to a silicon atom directly or via another functional group.

3. The release film according to claim 1, wherein the release film is formed by applying the aqueous coating composition to a substrate film before the crystal orientation is completed, stretching the substrate film in at least one direction, and then heat-treating the substrate film to complete the crystal orientation of the substrate film.

4. The release film according to claim 1, wherein the polyester film has a surface layer that is substantially free of inorganic particles, and the release layer is formed on the surface layer.

5. The release film according to claim 1, which is a release film for use in the manufacture of multilayer ceramic capacitors or resin sheets.

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