Release film

Abstract

The present invention provides a release film that can reduce the amount of organic solvent used, and that has both easy releasability and good wettability, particularly for thin ceramic green sheets, and that also has excellent adhesion between the substrate film and the release layer. The release film of the present invention is a release film having a release layer on at least one surface of a polyester film, the release layer being formed by reacting and solidifying an aqueous coating composition, and the aqueous coating composition is composed of (a) a first resin having a siloxane structure with an alkenyl group, (b) a second resin containing a hydrogen group, and SiO 4 / 2 and (c) a silicone emulsion containing a third resin containing a silicone having Q units represented by the formula:

Description

[Technical Field]

[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. [Background technology]

[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 ceramic capacitors, ceramic substrates, etc. In recent years, as multilayer ceramic capacitors have become smaller and their capacity has increased, the thickness of ceramic green sheets has also tended to become thinner. 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 it. 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.

[0004] Patent Documents 1 and 2 propose release films produced by a method (hereinafter referred to as "offline coating") in which a coating composition containing a polysiloxane having an unsaturated group, a polysiloxane having a hydrogen 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 Document 3 proposes a release film in which a release layer is formed by applying an aqueous coating composition containing an alkenyl group-containing silicone and a silicone containing a hydrogen group and a phenyl group 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 offline coating using a coating composition containing a silicone containing an aryl group. Furthermore, Patent Document 5 proposes a release film in which a release layer is formed by inline coating using a coating composition containing a silicone having a Q unit. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-292894 [Patent Document 2] International Publication No. WO2017 / 200056 [Patent Document 3] Patent No. 5735278 [Patent Document 4] Patent No. 5756315 [Patent Document 5] Patent Publication No. 2021-11081 Summary of the Invention [Problem to be solved by the invention]

[0008] 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.

[0009] 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 the conveyance process of the release film.

[0010] 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.

[0011] In Patent Documents 1 and 2, the releasability and wettability of the thin ceramic green sheets are particularly insufficient, and there is a need for a combination of easy releasability and good wettability. 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.

[0012] In addition, the drying equipment for organic solvents must be explosion-proof, which increases the initial installation costs, and the large amount of energy required to operate it results in large CO2 emissions and a large environmental impact, which are issues.

[0013] The release film described in Patent Document 3 has a release layer formed by in-line coating, but it was not envisioned for use in molding ceramic green sheets, and there were issues with the releasability of thin ceramic green sheets in particular. Furthermore, a phenyl group-containing crosslinking agent was used to improve the adhesion between the substrate and the release layer, but the effect of the phenyl group on the release force was not recognized, and the film was unsuitable as a release film with easy releasability.

[0014] The release film described in Patent Document 4 has a release layer formed from a siloxane having an aryl group and a crosslinking agent. However, the invention of Patent Document 4 had problems with the adverse effects on the human body and the large environmental impact during the manufacturing process. Furthermore, because the release film contains a bulky substituent such as an aryl group, the steric hindrance makes it difficult for the curing reaction of the release layer to proceed. When the coating composition was cured at 135°C as described in the examples, the amount of heat required for curing the release layer was insufficient, which could adversely affect releasability. To further promote the curing of the release layer, it was necessary to cure the release layer at a higher temperature. However, the invention of Patent Document 4 required production at a relatively low temperature due to the risk of thermal deformation of the substrate film during the manufacturing process.

[0015] The release film described in Patent Document 5 has a release layer formed by in-line coating that combines releasability and wettability. For example, technological development related to thin ceramic green sheets is constantly progressing, and there is a demand for even easier releasability and improved adaptability to thin ceramic green sheets than at the time of filing of Patent Document 5. There is also a demand for further improvement in the substrate adhesion of the release layer, and for reducing adverse effects such as heavy release caused by the release layer falling off the substrate film during the production process of the release film or the molding process of the resin sheet, for example, the ceramic green sheet. In particular, when a silicone resin containing Q units is used, the release layer formation product is difficult to follow when the substrate film is stretched, and there is a risk of poor substrate adhesion due to the stress difference between the release layer and the substrate film.

[0016] 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. [Means for solving the problem]

[0017] 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.

[0018] That is, the present invention comprises the following:

[0019] [1] A release film having a release layer on at least one surface of a polyester film, The release layer is a layer formed by reacting and solidifying an aqueous coating composition, The aqueous coating composition contains a silicone emulsion containing the following resin: a release film, the aqueous coating composition further comprising a substrate adhesion promoter: (a) a first resin having a siloxane structure represented by Structural Formula 1; [ka]

[0020] (In Structural Formula 1, R1 is an alkenyl group having 2 to 8 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 8 carbon atoms, and k is 1 to 50.) (b) a second resin containing a hydrogen group; and SiO 4 / 2 (c) a third resin containing a silicone having Q units represented by the formula:

[0021] [2] The release film according to [1], wherein the substrate adhesion promoter is a water-soluble or water-dispersible silane coupling agent having a hydrolyzable group and an organic functional group bonded to a silicon atom directly or via a bonding group.

[0022] [3] The (a) first resin and / or the (b) second resin further have a siloxane structure represented by the following structural formula 2: [ka]

[0023] (In structural formula 2, R3 is an alkyl group having 1 to 4 carbon atoms, Ar is an aryl group, and m is 1 or more and 50 or less), the release film according to [1] or [2].

[0024] [4] The release film according to any one of [1] to [3], wherein the second resin (b) has a structure represented by the following chemical formula 2:

[0025] [ka]

[0026] (In chemical formula 2, l is 1 or more and 50 or less, m is 1 or more and 50 or less, and n is 0 or more and 5 or less) [5] The release film according to any one of [1] to [4], 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. [6] The release film according to any one of [1] to [5], which is a release film for use in producing a ceramic capacitor or a resin sheet. [Effects of the Invention]

[0027] The release film of the present invention can improve the releasability and wettability of the release layer, and further can suppress the occurrence of defects in thin resin sheets, particularly ceramic green sheets.

[0028] Furthermore, the harmful effects on the human body and the environmental load during the manufacturing process can be reduced. It is possible to form a release layer that is free from the risk of deterioration in the adhesive strength between the substrate film and the release layer, particularly in the immediate adhesiveness to the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0029] 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.

[0030] 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.

[0031] Furthermore, there is no need to use explosion-proof equipment for drying organic solvents, and compared to conventional manufacturing equipment, energy consumption during operation is reduced, which in turn reduces CO2 emissions and the environmental impact.

[0032] Furthermore, according to the present invention, by using a silicone emulsion containing a silicone resin of a specific structure and composition, it is possible to provide a release film with better releasability than release films produced by conventional in-line coating. In particular, by using a release layer containing a cured product of silicone having Q units, it is possible to obtain a release film with excellent releasability and wettability. Furthermore, by using a release layer containing a cured product of silicone that further contains a siloxane structure having an aryl group, it is possible to improve light releasability. Furthermore, it is possible to obtain a release film with excellent substrate adhesion.

[0033] Furthermore, according to the present invention, since an aqueous coating composition containing a substrate adhesion promoter is used, a release film having excellent substrate adhesion can be obtained. In particular, when a release layer containing a silicone resin having Q units is produced by in-line coating, there is a difference in extensibility between the substrate film and the release layer-formed product, and immediate adhesion to the substrate immediately after the release layer is cured is required. In the present invention, by including a substrate adhesion promoter, a release film having excellent immediate adhesion to a substrate can be obtained.

[0034] The present invention relates to a release film having a release layer on at least one surface of a polyester film, the release layer being formed by reacting and solidifying an aqueous coating composition, the aqueous coating composition containing a silicone emulsion, the silicone emulsion containing the following, and the aqueous coating composition further containing a substrate adhesion promoter:

[0035] (a) a first resin having a siloxane structure represented by structural formula 1;

[0036] [ka]

[0037] (In Structural Formula 1, R1 is an alkenyl group having 2 to 8 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 8 carbon atoms, and k is 1 to 50.) (b) Second resin containing hydrogen groups SiO 4 / 2 (c) a third resin containing a silicone having a Q unit represented by

[0038] 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, thereby suppressing defects such as pinholes.

[0039] The present invention can also achieve the following effects: In the present invention, an aqueous coating composition containing a significantly reduced amount of organic solvent compared to conventional coating compositions, or an aqueous coating composition containing substantially no organic solvent, is used, so that a release film can be produced that is less harmful to the human body and less environmentally hazardous, while suppressing CO2 generation.

[0040] Furthermore, in one embodiment, the release film of the present invention can be formed by applying an aqueous coating composition containing a silicone emulsion having a predetermined composition by inline coating to form a release layer, thereby achieving a release layer that not only has excellent releasability and wettability but also excellent substrate adhesion. More specifically, the inclusion of a silicone emulsion containing silicone having Q units allows for a structure in which siloxane bonds are extended three-dimensionally, and a crosslinking reaction occurs between the alkenyl group in the silicone molecule having Q units and the silicone having a hydrogen group, resulting in a dense crosslinked structure, resulting in a release layer that has excellent solvent resistance and easy releasability. Furthermore, the inclusion of Q units reduces the hydrophobicity of the release layer surface, allowing for a release layer that also has excellent wettability.

[0041] Furthermore, by including a silicone emulsion containing a silicone containing a siloxane structure having an aryl group, the adhesion strength can be improved due to the intermolecular interaction between the aryl group in the base film and the release layer. Furthermore, by using a bulky substituent such as an aryl group, the curing reaction of the release layer can be delayed, and the curing reaction can be prevented from progressing when the base film is stretched after application of the coating composition, and can be promoted when the crystal orientation after stretching is completed. By not allowing the curing reaction to proceed when the base film is stretched, the stress generated by the difference between the stretchability of the base film and the stretchability of the coating composition can be reduced, and a decrease in adhesion to the base film can be prevented.

[0042] In particular, in the present invention, by including the first resin, the second resin, and the third resin, the above-mentioned effects can be more effectively exhibited.

[0043] In the present invention, the reaction retardation effect of the aryl group can improve the adhesion of the release layer to the substrate. For example, in order to improve the adhesion of the release layer to the substrate, it is preferable that the curing reaction proceeds after the substrate film is stretched.

[0044] Furthermore, by using an aqueous coating composition containing a substrate adhesion promoter, a release layer with excellent immediate adhesion to the substrate immediately after formation can be obtained. The present invention, which has excellent immediate adhesion, can prevent a portion or most of the release layer from peeling off from the substrate, for example, when peeling off various resin sheets laminated on a release film. This can avoid the problem of release layer components being mixed into the resin sheet. Furthermore, peeling of the release layer from the substrate film during the release film transport process in various resin sheet molding processes can also be prevented.

[0045] Furthermore, since the present invention has excellent immediate adhesion to the substrate, it is possible to prevent a portion of the release layer from being transferred to the transport roll during the production process of the release film, and when the release film is wound into a roll, it is possible to avoid the risk of the release layer being transferred to the back surface of the release film that comes into contact with the release layer. If the release layer is transferred to the conveying roll or the release film is transferred to the back surface, the coating uniformity of the release layer may deteriorate, the thickness of the release layer may decrease, defects may occur on the surface of the release layer, and heavy peeling may occur. Therefore, the present invention can solve such problems.

[0046] In the present invention, immediate adhesion means the adhesion of the release layer to the substrate immediately after the release layer is formed using the aqueous coating composition, and means, for example, adhesion within a range of 1 second to 24 hours after the release layer is formed. The immediate adhesion may also be measured after the film is wound into a roll.

[0047] As will be described later, it is difficult to structurally identify 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, and in the present invention, it has been discovered that "it is good for the curing reaction to proceed after the base film is stretched."

[0048] (polyester film) The polyester constituting the polyester film used as the base film is not particularly limited, and a film of 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 contain small amounts of other dicarboxylic acid components or diol components. For example, from a cost perspective, polyethylene terephthalate produced solely from terephthalic acid and ethylene glycol is preferred. Furthermore, known additives, such as antioxidants, light stabilizers, UV absorbers, and crystallization agents, may be added within limits that do not impair the effects of the release film of the present invention. The polyester film is preferably a biaxially oriented polyester film due to its high bidirectional elastic modulus.

[0049] 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. An intrinsic viscosity of 0.50 dL / g or more is preferred because it prevents frequent breakage during the stretching process. Conversely, an intrinsic viscosity of 0.70 dL / g or less is preferred because it allows for good cuttability when cut to a specified product width and prevents dimensional defects. It is also preferred that the raw material pellets are thoroughly vacuum dried.

[0050] In this specification, when simply referring to a "polyester film", it may refer to a polyester film having (laminated with) a surface layer A and a surface layer B.

[0051] 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.

[0052] 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, and the stretching is preferably 1 to 8 times, particularly 2 to 6 times, in both the longitudinal and transverse directions.

[0053] 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 impact.

[0054] 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.

[0055] 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. By making the surface layer A 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.

[0056] In one embodiment, the surface layer A does not contain particles with a particle size of less than 1.0 μm, so that problems caused by the shape of particles in the substrate being transferred to the resin sheet can be more effectively prevented.

[0057] 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 one in which the surface layer A substantially free of particles less than 1.0 μm in diameter also substantially free of particles 1.0 μm or larger in diameter.

[0058] 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.

[0059] 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.

[0060] In terms of 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 be a multi-layer structure. Furthermore, the surface layer B may not contain inorganic particles. In that case, it is preferable to provide a coating layer containing inorganic particles and a binder on the surface layer B to impart slip properties for winding the film into a roll.

[0061] 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, particularly 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.

[0062] In this case, the area surface average roughness (Sa) of the film of surface layer B is preferably in the range of 1 nm to 40 nm, more preferably in the range of 5 nm to 35 nm. When the total amount 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 amount 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.

[0063] 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. 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.

[0064] 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, and 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.

[0065] From the viewpoint of reducing pinholes, it is preferable that recycled raw materials are not used for the surface layer A, which is the layer on which the release layer is to be formed, in order to prevent the inclusion of inorganic particles such as lubricants.

[0066] 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 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 thickness of the base film, the proportion of recycled materials used in the surface layer B can be increased, which is preferable as it reduces the environmental impact.

[0067] From an economical standpoint, 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 lubricant contained in layer B, its particle size, and the area surface average roughness (Sa) satisfy the above ranges.

[0068] Furthermore, in order to improve the adhesion of a release layer or the like to be applied later, or to prevent static electricity, 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.

[0069] 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 easy-adhesion layers include layers 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.

[0070] (Release layer) In the present invention, the release layer is 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 a silicone emulsion and a substrate adhesion promoter, and the silicone emulsion contains the following: (a) a first resin having a siloxane structure represented by Structural Formula 1;

[0071] [ka]

[0072] (In Structural Formula 1, R1 is an alkenyl group having 2 to 8 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 8 carbon atoms, and k is 1 to 50.) (b) a second resin containing a hydrogen group; SiO 4 / 2 (c) a third resin containing a silicone having a Q unit represented by Here, the first resin and / or the second resin further has a siloxane structure represented by the following structural formula 2.

[0073] [ka]

[0074] (In Structural Formula 2, R3 is an alkyl group having 1 to 4 carbon atoms, Ar is an aryl group, and m is 1 or more and 50 or less.)

[0075] The release layer having these characteristics can provide a release film with excellent releasability and wettability, can suppress the occurrence of defects such as pinholes in resin sheets or ceramic green sheets, and can form sheets with a uniform thickness. Furthermore, a release layer with excellent substrate adhesion can be provided, and can suppress the release layer from falling off during the process for producing the release film or the process for producing the resin sheet or ceramic green sheet. Furthermore, by using a release layer made of a cured product containing a substrate adhesion promoter, a release layer with excellent immediate adhesion to the substrate can be provided.

[0076] The aqueous coating composition of the present invention is a composition containing a silicone emulsion. The silicone emulsion contains (a) a first resin, (b) a second resin, and (c) a third resin, and in one embodiment, a fourth resin (d). A silicone emulsion refers to a composition in which these water-insoluble resins are dispersed in water with a surfactant. The aqueous coating composition may contain one or more types of silicone emulsion. The silicone emulsion may contain only one or more of the resins (a) the first resin, (b) the second resin, (c) the third resin, and (d) the fourth resin. Alternatively, the silicone emulsion may contain all of the resins (a), (b), (c), and (d) in a single silicone emulsion.

[0077] The aqueous coating composition preferably contains substantially no organic solvent and uses water as a dispersion medium. The absence of organic solvent improves the stability of the silicone emulsion, preventing changes in the composition of the aqueous coating composition due to emulsion breakdown, and preventing aggregation and gelation of the resin in the silicone emulsion.

[0078] "Substantially free of organic solvents" means, for example, a content of 10,000 ppm or less, preferably 5,000 ppm or less, more preferably 3,000 ppm or less, and most preferably below the detection limit, based on the total weight of the aqueous coating composition. This is because, even if no organic solvent is intentionally used, small amounts of organic solvents used in the polymerization process of the resin contained in the silicone emulsion or the emulsification process of the emulsion may remain.

[0079] ((a) First Resin) The (a) first resin contained in the silicone emulsion preferably has the following structure:

[0080] [ka]

[0081] (In Structural Formula 1, R1 is an alkenyl group having 2 to 8 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 8 carbon atoms, and k is 1 to 50.) By including structural formula 1, the crosslinking reaction between the silicone having an alkenyl group and a hydrogen group progresses, resulting in a release layer with high crosslink density and excellent solvent resistance, demonstrating easy releasability.

[0082] Examples of the alkenyl group 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.

[0083] (a) The first resin may have a structure represented by the following chemical formula 1, for example.

[0084] [ka]

[0085] In the above chemical formula 1, R1 is an alkenyl group having from 2 to 8 carbon atoms, and R2 is an alkyl group having from 1 to 4 carbon atoms or an alkenyl group having from 2 to 8 carbon atoms. R1 is preferably a vinyl group, and R2 is preferably a methyl group. R2 may be the same or different, and for example, a structure in which R2 at both ends are methyl groups and only R2 in the side chain has a vinyl group is preferred. k is a structure that contributes to the crosslinking reaction and is preferably from 1 to 50. o is a structure that contributes to releasability and is preferably from 1 to 500. k is preferably 1 or more because the crosslinking reaction proceeds, and if it is 50 or less, unreacted alkenyl groups are less likely to remain in the release layer, resulting in excellent releasability. If o is 1 or more, releasability is preferably exhibited, and if it is 500 or less, there is no risk of the crosslinking density decreasing, so it is preferred.

[0086] As illustrated in Chemical Formula 1, SiO 2 / 2From the viewpoint of releasability, it is preferable that the silicone is composed of D units represented by the following formula: In general, silicones composed of D units tend to have a helical structure in the siloxane bond, and in the case of polydimethylsiloxane, for example, the two methyl groups present in the siloxane bond are all aligned on the outside of the molecular chain, which makes the silicone hydrophobic and results in a release layer with excellent releasability, which is preferable.

[0087] In one embodiment, the first resin contained in the silicone emulsion preferably further has the following structural formula 2:

[0088] [ka]

[0089] (In Structural Formula 2, R3 is an alkyl group having 1 to 4 carbon atoms, Ar is an aryl group, and m is 1 or more and 50 or less.) By including an aryl group, which is a bulky substituent, as shown in structural formula 2, the curing reaction of the release layer is delayed, and curing of the release layer is completed when the crystal orientation of the substrate film is completed after stretching. The delay in the curing reaction makes it difficult for the release layer to proceed with curing when the substrate film is stretched, which maintains the stretchability of the coating composition and is preferable because there is no risk of a decrease in adhesion due to the stress difference between the substrate film and the release layer. Furthermore, the resulting release layer is free of defects such as coating film cracking that occur during stretching, and has excellent releasability, which is also preferable.

[0090] As described above, the (a) first resin may have structural formula 2. In another embodiment, the (b) second resin contained in the silicone emulsion described below may have the structure of the above structural formula 2. For example, if the (b) second resin has an aryl group and the (a) first resin does not have an aryl group, the (a) first resin is more likely to be localized on the surface side of the release layer during at least one step of stretching the substrate film or drying and curing the coating composition, and a release layer with excellent releasability can be obtained, which is preferable.

[0091] Examples of the aryl group include a phenyl group, a benzyl group, a tolyl group, and a xylyl group, with a phenyl group being particularly preferred.

[0092] The number average molecular weight of the (a) first resin is preferably 1,000 or more and less than 30,000, more preferably 2,000 or more and less than 15,000, and even more preferably 3,000 or more and less than 10,000. If the number average molecular weight is 1,000 or more, it is likely to be localized on the surface of the release layer, making it easier to obtain sufficient releasability. On the other hand, if the number average molecular weight is less than 30,000, the emulsification properties of the silicone emulsion tend to be good, and uniform coating properties also tend to be good. The number average molecular weight in the present invention is 1 H NMR and 29 The siloxane structure is identified from the peaks observed in Si NMR, and the ratio is calculated from the integral ratio of the peaks derived from each siloxane structure.

[0093] The content of the first resin contained in the silicone emulsion in the aqueous coating composition is preferably 5% by mass or more and 70% by mass or less, more preferably 7% by mass or more and 60% by mass or less, and even more preferably 10% by mass or more and 55% by mass or less, when the total solids weight in the coating composition is taken as 100. A content of 5% by mass or more is preferred because the amount of (a) first resin, which exhibits releasability by localizing on the release layer surface, is sufficient, resulting in excellent releasability. A content of 70% by mass or less is preferred because it prevents the increase in uncrosslinked components, which can cause heavy releasability. The amount of silicone emulsion in the aqueous coating composition can be appropriately adjusted so that the content of the first resin falls within the above range.

[0094] In the present invention, the total solids weight in the coating composition that forms the release layer refers to the total solids weight of (a), (b), (c), the substrate adhesion promoter, and (d) that is used as needed.

[0095] ((b) Second Resin) The hydrogen group-containing second resin (b) may be any compound having a siloxane bond in the main chain, but is preferably a polyorganosiloxane having a hydrogen group at the end or side chain, and more preferably polydimethylsiloxane. The terminal silicon atom may have a hydrogen group, but is preferably a trialkylsilane structure such as trimethylsilane, and preferably has 2 to 50 hydrogen groups per molecule. The presence of two or more hydrogen groups results in a release layer with a high crosslink density when cured, exhibiting easy releasability.

[0096] In one embodiment, the second resin has a structure represented by the following Chemical Formula 2.

[0097] [ka]

[0098] In Chemical Formula 2, l is 1 to 50, m is 1 to 50, and n is 0 to 5. When l is 1 to 50, the crosslinking reaction between the alkenyl groups and hydrogen groups in the coating composition proceeds, resulting in a release layer with high crosslink density and excellent solvent resistance. When m is 1 to 50, the bulky phenyl group delays the reaction during curing of the release layer, resulting in a release layer with good stretchability and excellent adhesion. Furthermore, the π electrons of the phenyl group interact with the substrate film, resulting in even better adhesion. When n is 0 to 5, the compatibility with the (a) first resin or the (d) fourth resin described below in the coating composition decreases, leading to localization of the (a) first resin or the (d) fourth resin on the surface side of the release layer. As a result, the release layer has excellent releasability, which is preferable.

[0099] The number average molecular weight of the second resin (b) in the present invention is preferably 1,000 or more and less than 10,000, more preferably 1,000 or more and less than 5,000, and even more preferably 1,500 or more and less than 3,000. 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 less than 10,000, the emulsification characteristics into the silicone emulsion 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 29 The siloxane structure is identified from the peaks observed in Si NMR, and the ratio is calculated from the integral ratio of the peaks derived from each siloxane structure.

[0100] The content of the second resin contained in the silicone emulsion in the aqueous coating composition is preferably 1% by mass or more and 50% by mass or less, more preferably 3% by mass or more and 40% by mass or less, and even more preferably 5% by mass or more and 35% by mass or less, when the total solid content of the coating composition is taken as 100. A content of 1% by mass or more is preferred because the crosslinking reaction proceeds sufficiently. A content of 50% by mass or less is preferred because it prevents the increase in unreacted components, which may cause heavy peeling.

[0101] The amount of silicone emulsion in the aqueous coating composition can be adjusted appropriately so that the amount of the second resin falls within the above range.

[0102] For example, when the (b) second resin contains an aryl group represented by structural formula 2, the content of the second resin is equal to or less than the content of the (c) third resin described below, and preferably the content of the second resin is 5% by mass or less less than the content of the (c) third resin described below, when the total solid content of the coating composition is taken as 100. By satisfying these conditions, the crosslinking reaction proceeds sufficiently, and there is no risk of unreacted components increasing, which may cause heavy peeling, which is preferable.

[0103] The structure containing the aryl group represented by Structural Formula 2 is preferably contained in the second resin (b) rather than the first resin (a) because this improves both adhesion and releasability. Specifically, it is believed that the inclusion of an aryl group in the second resin (b), which acts as a crosslinking agent, reduces compatibility with the first resin (a). This leads to increased localization of (a) on the surface of the release layer during stretching of the substrate film or drying and curing of the coating composition, thereby improving releasability. On the other hand, in the present invention, the curing reaction caused by the aryl group contained in the second resin (b), which acts as a crosslinking agent, can be appropriately controlled, thereby increasing the interaction between the substrate film and the release layer and improving adhesion. Thus, the present invention can solve the conventional problems of excessively delayed curing reactions, which require a long time for the release layer to cure, and also of rapid curing reactions that make it difficult to obtain the desired release layer.

[0104] In another embodiment, the structure containing an aryl group represented by Structural Formula 2 may be present in both (a) the first resin and (b) the second resin.

[0105] ((c) Third Resin) The silicone emulsion in the aqueous coating composition of the present invention contains SiO 4 / 2 It is preferable that the emulsion contains a (c) third resin containing a silicone having a Q unit represented by the formula: The silicone emulsion containing the (c) third resin is a water-dispersed silicone having the structure in the form of an emulsion or colloid. The silicone having the structure may be any structure as long as it is a compound having a siloxane bond in the main chain, but polyorganosiloxanes having alkenyl groups at the terminal and / or side chain are preferred. Furthermore, copolymers containing dialkylsiloxane units or alkylphenylsiloxane units are preferred because they can easily adjust the amount of alkenyl groups in one molecule while exhibiting release properties. The terminal silicon atom preferably has an alkenyl group, but may also be a trialkylsilane structure such as trimethylsilane.

[0106] SiO 4 / 2Examples of silicones having Q units represented by the formula (3) include those having the structure represented by the formula (3) below.

[0107] R4 a R5 b SiO (4-a-b) / 2 ...(chemical formula 3) (In Chemical Formula 3, R4 is an alkenyl group having 2 to 8 carbon atoms, R5 is a monovalent saturated hydrocarbon group having 1 to 16 carbon atoms selected from an alkyl group or an aryl group, a is an integer of 0 to 3, and b is an integer of 0 to 3 that satisfies a+b≦3.) Here, Chemical Formula 3 shows a general formula, and the structural unit where a = 0 and b = 0 is the Q unit, and (c) the third resin has this Q unit. Furthermore, the structural unit where a = 1 or a = 2 is a siloxane structure having an alkenyl group, and the structural unit where b = 2 is a siloxane structure having only an alkyl group or an aryl group in the side chain, and these siloxane structures may be present. Furthermore, the structural unit where a + b = 3 represents a siloxane structure having a terminal group.

[0108] Examples of alkenyl groups having 2 to 8 carbon atoms represented by R4 include vinyl, allyl, butenyl, pentenyl, and hexenyl groups, with vinyl being particularly preferred. Examples of alkyl groups represented by R5 include methyl, ethyl, propyl, and butyl groups, and examples of aryl groups include phenyl and tolyl groups. It is preferable that (c) contains an alkenyl group having 2 to 8 carbon atoms represented by R4, from the viewpoint of reactivity with hydrogen groups. The fewer the carbon atoms, the less the influence of steric hindrance and the more excellent the reactivity, and a vinyl group having 2 carbon atoms is the most preferred. It is preferable that 50 mol % or more of the substituents of R5 are methyl groups, from the viewpoint of easy peelability.

[0109] Silicone containing Q units can have a structure in which the siloxane bond is expanded three-dimensionally, and therefore the alkenyl groups in the molecule can also be spread three-dimensionally. Therefore, by reacting the (b) second resin, which is a silicone having a hydrogen group, with the alkenyl groups in the (c) molecule, a dense crosslinked structure can be formed, and a release layer with excellent solvent resistance can be obtained. Generally, the SiO contained in the release layer 2 / 2 As the ratio of D units, expressed as [D], increases, the siloxane bond tends to take on a helical structure. For example, in the case of polydimethylsiloxane, the two methyl groups present in the siloxane bond are all arranged on the outside of the molecular chain, making the material hydrophobic. On the other hand, as the ratio of Q units contained in the release layer increases, the helical structure of the siloxane bond formed from the D units collapses, reducing hydrophobicity. While not limited by theory, by using a release layer containing silicone with Q units, it is possible to achieve both easy release properties due to increased crosslink density and reduced hydrophobicity due to the collapse of the helical structure of the siloxane bond, i.e., excellent wettability.

[0110] The content of the (c) third resin in the silicone emulsion in the aqueous coating composition is 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 65% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less, when the total solid content of the coating composition is taken as 100. A content of 10% by mass or more is preferred because the silicone having Q units disrupts the helical structure of the silicone consisting of D units contained in the release layer, resulting in a release layer with excellent wettability. A content of 70 parts by mass or less is preferred because the silicone having Q units does not disrupt the helical structure of the silicone consisting of D units contained in the release layer too much, resulting in a release layer with excellent releasability.

[0111] The content of Si atoms in the Q unit is SiO 4 / 2The content of Si atoms in the silicone having Q units represented by the formula (I) is 0.05 to 60 mol %, preferably 0.1 to 55 mol %, and more preferably 1.0 to 50 mol % relative to the total Si atoms in the silicone having Q units represented by the formula (I). When the content of Si atoms in the Q units is 0.05 mol % or more, the siloxane bonds can assume a structure that is sufficiently extended three-dimensionally, which is preferable because it exhibits the effect of increasing crosslink density. When the content is 60 mol % or less, excessive wettability is not imparted, which is also preferable because there is no risk of severe peeling.

[0112] (b) From the viewpoint of forming a dense crosslinked structure by the reaction with the second resin, the content of Si atoms contained in the siloxane structure having an alkenyl group is SiO 4 / 2 It is preferably 0.1 to 30 mol %, more preferably 1 to 20 mol %, based on all Si atoms in the silicone having Q units represented by the following formula:

[0113] It is preferable that the silicone having Q units is solid at room temperature. The fact that the silicone having Q units is solid at room temperature means that many Q units exist as continuous bonds in the molecule, and the silicone has a rigid molecular skeleton and exhibits physical properties similar to glass. By using a release layer containing such a silicone having a rigid molecular skeleton, the elastic modulus of the release layer is increased, and the release layer is less likely to deform when peeling off an object to be peeled, such as a ceramic green sheet, and the release layer exhibits easy peelability, which is preferable.

[0114] As mentioned above, silicones containing Q units have a rigid molecular skeleton, which results in poor stretchability and may cause coating film cracking or reduced adhesion to the substrate due to stretching. However, in the present invention, a silicone emulsion containing an aryl group represented by structural formula 2 is used as the coating composition, and its reaction delay effect makes it difficult for the crosslinking reaction to proceed when the substrate film is stretched, so that even a release layer containing a silicone containing Q units can be formed without poor adhesion or coating defects. Furthermore, because the silicone contains a substrate adhesion promoter, a release layer with excellent immediate adhesion to the substrate can be formed.

[0115] ((d) Fourth Resin) By including in the silicone emulsion in the aqueous coating composition of the present invention a fourth resin (d) having alkenyl groups at only both ends, it is possible to obtain a release film that has both releasability and wettability and also has excellent adhesion to the substrate.

[0116] (d) Examples of the fourth resin include those shown in Chemical Formula 4 below.

[0117] [ka]

[0118] In Chemical Formula 4, R1 is an alkenyl group having 2 to 8 carbon atoms, and p is 1 or more and 300 or less. When p is within the above range, it is preferable because it exhibits excellent releasability. (d) The fourth resin has alkenyl groups only at both ends, so that the D units are connected in a linear chain, and the helical structure is not destroyed by a crosslinking reaction, and it exhibits superior releasability to (a) the first resin.

[0119] However, in an embodiment including a fourth resin having alkenyl groups only at the molecular terminals, the amount of alkenyl groups is less than that of the (a) first resin, so the crosslinking density may decrease, but at the same time, the crosslinking reaction with the silicone (a) first resin having alkenyl groups in its side chain present in the release layer can prevent deterioration of solvent resistance. Without being limited by theory, the release film of the present invention can realize a release layer with excellent releasability by localizing the silicone (d) fourth resin having alkenyl groups only at both terminals in the surface layer of the release layer and forming a release layer bonded to the silicone (c) having Q units and alkenyl groups via the (a) first resin having alkenyl groups in its side chain.

[0120] The number average molecular weight of the fourth resin contained in the silicone emulsion of the present invention is preferably 1,000 or more and less than 10,000, more preferably 1,000 or more and less than 5,000, and even more preferably 1,500 or more and less than 3,000. 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 less than 10,000, the emulsification characteristics into the silicone emulsion 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 29 The siloxane structure is identified from the peaks observed in Si NMR, and the ratio is calculated from the integral ratio of the peaks derived from each siloxane structure.

[0121] The content of the fourth resin contained in the silicone emulsion in the aqueous coating composition is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 35% by mass or less, when the total solid content of the coating composition is taken as 100. A content of 1% by mass or more is preferred because it can be localized on the surface of the release layer and exhibit releasability. A content of 50% by mass or less is preferred because the crosslink density of the release layer decreases, preventing the risk of heavy releasability. The amount of silicone emulsion in the aqueous coating composition can be adjusted appropriately so that the amount of the fourth resin falls within the above range.

[0122] (Substrate adhesion promoter) In the present invention, the substrate adhesion promoter is not particularly limited, but is preferably one having a structure having a hydrolyzable group and an organic functional group bonded to a silicon atom directly or via a bonding group, and is more preferably a water-soluble or water-dispersible silane coupling agent.

[0123] Examples of the substrate adhesion promoter include compounds represented by the following chemical formula. YSiX3 (chemical formula 5) Here, Y is 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. Y may be bonded directly to the Si element, or may be bonded via, for example, an alkyl group having 1 to 10 carbon atoms, an ether group, or an oxyalkylene group.

[0124] 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. As the hydrolyzable group, a methoxy group or an ethoxy group is preferred.

[0125] Preferred substrate adhesion promoters include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, and vinylmethyldimethoxysilane.

[0126] 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 Chemical Formula 5, and a combination of a silane coupling agent in which an epoxy group is incorporated into Y and a silane coupling agent in which a vinyl group is incorporated into Y is more preferred. The 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 into Y and a silane coupling agent in which a vinyl group is incorporated into 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.

[0127] The content of the adhesion promoter to the substrate is preferably 0.01 to 15 parts by mass, more preferably 0.05 to 10 parts by mass, and most preferably 0.1 to 8 parts by mass, when the weight of the total solid content forming the release layer is 100 parts by mass. If the content of the adhesion promoter is 0.01 to 15 parts by mass, the adhesion of the release layer to the substrate, particularly immediate adhesion to the substrate, is good.

[0128] In this case, the total solid weight of the release layer refers to the total solid weight of (a), (b), (c), the substrate adhesion promoter, and (d) used as needed.

[0129] (surfactant) The aqueous coating composition of the present invention preferably contains 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.

[0130] When a surfactant is contained, the surfactant may segregate toward the substrate during the drying and curing process of the aqueous coating composition after application to the substrate, resulting in a deterioration in substrate adhesion. However, in the present application, an aqueous coating composition containing a substrate adhesion promoter is used, so that a release layer can be provided that does not deteriorate substrate adhesion.

[0131] Although known surfactants can be used without any particular limitations, it is preferable to use a surfactant that can be reduced in volatilization during the heating process for stretching and crystallizing the substrate film and remains in the release layer. The surfactant remaining in the release layer is preferable because it enhances wettability with ceramic slurries that use organic solvents.

[0132] As the surfactant, cationic, anionic, and nonionic surfactants can be suitably used, but nonionic surfactants are preferred from the viewpoint of improving 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 the Griffin formula.

[0133] Alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide. Examples of suitable nonionic emulsifiers include polyoxyethylene lauryl ether and polyoxyethylene tridecyl ether, and one or more of these may be used. When multiple emulsifiers are used, they may be added in either a block or random manner, but the HLB value is preferably in the range of 8 to 18, and more preferably in the range of 10 to 15. Of these nonionic emulsifiers, preferred examples include polyoxyethylene lauryl ether and polyoxyethylene tridecyl ether. If a nonionic emulsifier with an HLB value outside this range is used as the emulsifier for a silicone aqueous dispersion, the emulsifying and dispersing power and the stability of the aqueous dispersion may decrease.

[0134] Examples of alkylene oxides used in the present invention include those having the structure shown in Chemical Formula 6 below. H 2m+1 C m -O-(CH2-CH2-O) n -H (Formula 6) (In Chemical Formula 6, 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.)

[0135] 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. Furthermore, 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 m and n can take any value within the range of 1 to 30, but the larger the number, the higher the molecular weight, which is preferable because the surfactant does not volatilize during the heat curing process of the coating composition and the stretching and crystallization process of the substrate film, and does not contaminate the release film production process.

[0136] The content of the surfactant in the aqueous coating composition is preferably 0.1 to 20 parts by mass, and more preferably 0.15 to 15 parts by mass, when the total weight of the solids forming the release layer is 100 parts by mass. An amount of 0.1 part by mass or more is preferred because it provides excellent coatability when applied to a polyester film. An amount of 20 parts by mass or less is preferred because there is no risk of excessive residual surfactant causing a decrease in substrate adhesion.

[0137] In this case, the total weight of solids forming the release layer refers to the total weight of solids of (a), (b), (c), the adhesion promoter, and (d) used as needed.

[0138] (curing catalyst) The aqueous coating composition of the present invention must contain a platinum catalyst to allow the addition reaction between the silicone having an alkenyl group and the silicone having a hydrogen group. Known platinum catalysts can be used, such as platinum chloride and chloroplatinic acid. Taking into account dispersibility in silicone, the platinum catalyst may be a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt catalyst). Uniform dispersion can be ensured by simultaneously dispersing the silicone during emulsification.

[0139] The amount of platinum catalyst is preferably in the range of 10 to 800 ppm by weight of platinum element relative to the total solid content forming the release layer. By setting the weight ratio within this range, silicone can be sufficiently cured and the generation of aggregates can be suppressed, resulting in a release film with excellent smoothness. A platinum element weight ratio of 800 ppm or less is preferable because it accelerates the addition reaction between alkenyl groups and hydrogen groups, preventing the generation of silicone aggregates. 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, a content of 10 ppm or more is preferable because the silicone addition reaction proceeds efficiently, resulting in sufficient curing of the release layer and easy releasability.

[0140] 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, based on the total weight 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.

[0141] 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.

[0142] (Other features of the release layer) The thickness of the release layer in the present invention, measured after drying and curing, is preferably 0.001 to 0.2 μm, and more preferably 0.005 to 0.1 μm. 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 therefore the coating property is excellent when applied to a substrate film.

[0143] (Release film manufacturing method) In one embodiment, the release layer is formed on at least one surface of the 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.

[0144] 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 equal to or higher than the lower limit, the film-forming properties tend to be good. When the solids concentration is equal to or lower than 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.

[0145] 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.

[0146] Here, polyester film before completion of crystal orientation includes unstretched film, uniaxially oriented film obtained by orienting unstretched film in either the longitudinal direction (hereinafter sometimes referred to as the direction of continuous film production, longitudinal direction, MD direction) or the transverse direction (hereinafter sometimes referred to as the direction perpendicular to the longitudinal direction, width direction, TD direction), and also film that has been stretched and oriented at a low ratio in both the longitudinal and transverse directions (biaxially stretched film before final re-stretching in the longitudinal or transverse direction to complete orientation crystallization).

[0147] 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.

[0148] 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.

[0149] 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 the first resin, second resin, third resin, and optionally fourth resin contained in the silicone emulsion are oriented and interact with each other.

[0150] For example, it is thought that during the process of drying the water in the aqueous coating composition, during stretching of the substrate film, or during hardening of the release layer, differences in compatibility and molecular weight between the first resin, the second resin, and the third resin make (a) more likely to localize on the surface side of the release layer, thereby improving releasability.

[0151] On the other hand, in the present invention, the curing reaction by the aryl group contained in the second resin (b), which acts as a crosslinking agent, can be appropriately controlled, and the increased interaction between the substrate film and the release layer improves the adhesion between them.Furthermore, the substrate adhesion promoter also improves immediate adhesion to the substrate.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] (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 formed by curing a resin sheet-forming composition containing a resin component and a crosslinking agent, and a resin sheet formed by melt casting or solution casting of 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.

[0157] 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.

[0158] (Ceramic green sheets and ceramic capacitors) Generally, a multilayer ceramic capacitor has a rectangular parallelepiped ceramic body. First internal electrodes and second internal electrodes are alternately arranged 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.

[0159] 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.

[0160] For example, when the release film for producing ceramic green sheets of the present invention is used, ceramic green sheets can be 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 mother laminate is obtained by appropriately stacking and pressing 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. 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. [Example]

[0161] 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.

[0162] (Release layer thickness) The release film was cut into triangular pieces and coated with a 2 nm thick Pt (platinum) layer on the surface. The resulting samples were fixed in a multiaxial embedding capsule, embedded in epoxy resin, and sliced ​​perpendicular to the film surface using an ULTRACUT-S microtome to obtain ultrathin samples with a height of 50 nm. The resulting ultrathin samples were then mounted on a grid and steam-stained with 2% osmic acid at 60°C for 2 hours. The film cross section was observed using a LEM-2000 transmission electron microscope at an accelerating voltage of 100 kV to measure the thickness of the release layer. Measurements were performed at 10 random points, and the average of the measurements was used as the thickness of the release layer.

[0163] (uniformity of release layer application) The release film obtained by winding into a roll was unwound and cut into A4 size sheets. The release layer surface was visually observed using a fluorescent lamp and a halogen light, and the number of agglomerated coating defects (number per A4 size sheet) was compared and evaluated according to the following criteria. ◎: No coating defects 〇: 1 to 2 coating defects △: 3 to 5 coating defects ×: 6 or more coating defects

[0164] (Adhesion to substrate) A release film roll prepared by the method described in the following examples was unwound within 30 minutes of completion and an A4 cut sample was taken and evaluated. The release surface of the release film was rubbed five 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 at the rubbed area. Evaluation was performed according to the following criteria depending on the degree of writing with the magic marker. ⊚: There is no difference between the non-abraded area and the abraded area, and repelling of the magic marker is observed on both. ◯: There is a difference between the non-abraded area and the abraded area, but repelling of the magic marker is observed in both areas. △: Repelling of the marker ink was observed in some of the rubbed areas, and most of the rubbed areas were wet with the marker ink. ×: The entire rubbed area is wet with the magic marker, and no repelling is observed.

[0165] (surface free energy) For samples that had been conditioned for 24 hours under conditions of 23°C and 50% RH, a contact angle meter (DMo-501, manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the static contact angle when water was dropped and allowed to stand for 30 seconds. Similarly, the static contact angles of ethylene glycol and methylene iodide were each measured, and the following simultaneous equations regarding the surface tension components of the release layer were established using the surface tension components of each liquid below (the measured liquids of water, ethylene glycol, and methylene iodide are designated 1, 2, and 3, respectively, γLD is the dispersion force component of the liquid, γLP is the polar force component of the liquid, γLH is the hydrogen bond component of the liquid, γL is the sum of the surface tension components of the liquid, γSD is the dispersion force component of the release layer, γSP is the polar force component of the release layer, and γSH is the hydrogen bond component of the release layer. θ represents the contact angle). (γSD·γLD1) 1 / 2 +(γSP·γLP1) 1 / 2 +(γSH·γLH1) 1 / 2 =γL1(1+cosθ1) / 2 (γSD·γLD2) 1 / 2 +(γSP·γLP2) 1 / 2 +(γSH·γLH2) 1 / 2 =γL2(1+cosθ2) / 2 (γSD·γLD3) 1 / 2 +(γSP·γLP3) 1 / 2 +(γSH·γLH3) 1 / 2 =γL3(1+cosθ3) / 2 The γLD, γLP, γLH, and γL of water, ethylene glycol, and methylene iodide are as shown in Table 1.

[0166] [Table 1]

[0167] Next, the surface free energy γS of the release layer surface was calculated from the values ​​of γSD, γSP, and γSH obtained above using the following formula. γS=γSD+γSP+γSH

[0168] (Ceramic sheet peelability) Slurry composition I, consisting of the materials listed below, was stirred and mixed for 10 minutes, and then dispersed for 10 minutes using a bead mill with zirconia beads of 0.5 mm diameter to obtain a primary dispersion. Slurry composition II, consisting of the materials listed below, was then added to the primary dispersion in a ratio of (slurry composition I):(slurry composition II) = 3.4:1.0, and secondary dispersion was performed for 10 minutes using a bead mill with zirconia beads of 0.5 mm diameter 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 manufactured by Sekisui Chemical Co., Ltd.) 16.3 parts by mass 1-Ethyl-3-methylimidazolium ethyl sulfate 0.5 parts by mass

[0169] Next, within 12 hours of winding the release film roll prepared as described in the Examples below, an A4-sized sample was unwound and collected. The release surface of the sample was coated with an applicator to a dry thickness of 2.0 μm. The sample was then 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 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 60°C, and a peel rate of 0.3 m / min. The peeling direction was determined by attaching double-sided adhesive tape (Nitto Denko Corporation, No. 535A) to a SUS plate attached to the peel tester, and then securing the release film by adhering the release film side to the double-sided tape. The ceramic green sheet side was then pulled and peeled off. Of the obtained measured values, the average value of the peel force at 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 1.0mN / mm 〇: 1.0mN / mm or more, less than 2.0mN / mm △: 2.0mN / mm or more ×: Unable to peel or ceramic sheet breaks when peeled.

[0170] (Silicone emulsion: a-1) Using an emulsifier capable of stirring the entire container (NP Labs, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of alkenyl group-containing silicone (o = 125, k = 4, number average molecular weight 9756) represented by chemical formula (a-1) and 2% by mass of polyoxyethylene lauryl ether (Kao Corporation, trade name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain a silicone emulsion (a-1) with a solids content of 20% by mass. The emulsion particle size was also adjusted by adjusting the stirring speed and stirring time during emulsification.

[0171] [ka]

[0172] (Silicone emulsion: b-1) Using an emulsifier capable of stirring the entire container (NP Labs, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of hydrogen- and phenyl-containing silicone (l = 21, m = 8, n = 4, number average molecular weight 2806) represented by chemical formula (b-1) and 2% by mass of polyoxyethylene lauryl ether (Kao Corporation, trade name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain a silicone emulsion (b-1) with a solids content of 20% by mass. The emulsion particle size was also adjusted by adjusting the stirring speed and stirring time during emulsification.

[0173] [ka]

[0174] (Silicone emulsion: b-2) Using an emulsifier capable of stirring the entire container (NP Labs, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of hydrogen- and phenyl-containing silicone (l = 40, n = 40, number average molecular weight 5522) represented by chemical formula (b-2) and 2% by mass of polyoxyethylene lauryl ether (Kao Corporation, trade name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain a silicone emulsion (b-2) with a solids content of 20% by mass. The emulsion particle size was also adjusted by adjusting the stirring speed and stirring time during emulsification.

[0175] [ka]

[0176] (Silicone emulsion: c-1) Using an emulsifying device capable of stirring the entire container (manufactured by NP Labs, device name: Ultra Planetary Mixer), SiO 4 / 2 A silicone emulsion (c-1) containing 98% by mass of silicone having Q units represented by the formula (I) and 2% by mass of polyoxyethylene lauryl ether (trade name "Emulgen 109P" manufactured by Kao Corporation) as a surfactant was mechanically emulsified in an aqueous medium to obtain a silicone emulsion (c-1) containing 20% ​​by mass of silicone having Q units in solid content. 4 / 2 Silicone having a Q unit represented by the general formula 3 is represented by the formula 3, where R4 is a vinyl group, R5 is a methyl group, and only one vinyl group is bonded to the Si atom to which the vinyl group is directly bonded, and SiO 4 / 2 The content of Si atoms bonded to vinyl groups relative to the total Si atoms in the silicone having Q units represented by the formula (3) was 5 mol %, and the content of Si atoms contained in the Q units was 40 mol %. That is, in Chemical Formula 3, R4 was a vinyl group, R5 was a methyl group, and the siloxane structure in which a = 1 and b = 1 was 5 mol %, the siloxane structure in which a = 0 and b = 0 was 40 mol %, and the siloxane structure in which R5 was a methyl group, a = 0 and b = 2 or 3 was 55 mol %. The emulsion particle size was adjusted by adjusting the stirring speed and stirring time during emulsification. The number average molecular weight was also adjusted to 200,000.

[0177] R4 a R5 b SiO (4-a-b) / 2 ...(chemical formula 3) (In Chemical Formula 3, R4 is an alkenyl group having 2 to 8 carbon atoms, R5 is a monovalent saturated hydrocarbon group having 1 to 16 carbon atoms selected from an alkyl group or an aryl group, a is an integer of 0 to 3, and b is an integer of 0 to 3 that satisfies a+b≦3.)

[0178] (Silicone emulsion: d-1) Using an emulsifier capable of stirring the entire container (NP Labs, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of silicone (p = 23, number average molecular weight 1888) with alkenyl groups at only both ends, represented by chemical formula (d-1), and 2% by mass of polyoxyethylene lauryl ether (Kao Corporation, product name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain a silicone emulsion (d-1) with a solids content of 20% by mass. The emulsion particle size was also adjusted by adjusting the stirring speed and stirring time during emulsification.

[0179] [ka]

[0180] (Substrate adhesion promoter: e-1) A 1:1 mixture by weight of 3-glycidyloxypropyltrimethoxysilane and triacetoxyvinylsilane was used.

[0181] (Substrate adhesion promoter: e-2) Triacetoxyvinylsilane was used.

[0182] <Preparation Example 1 of Aqueous Coating Composition> An aqueous coating composition was obtained by mixing silicone emulsion (a-1), silicone emulsion (b-1), silicone emulsion (c-1), silicone emulsion (d-1), substrate adhesion promoter (e-1), and water in the proportions shown in Table 2 to a solids concentration of 4 mass%. At this time, 0.02 mass% of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd., product name: CAT-PM-10A) and 150 ppm of a crosslinking reaction inhibitor (1-ethynylcyclohexanol) were mixed in relative to the total weight of the aqueous coating composition.

[0183] <Aqueous Coating Composition Production Examples 2 to 8> An aqueous coating composition was obtained in the same manner as in Production Example 1, except that the ingredients were mixed to the types and ratios shown in Table 2.

[0184] 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 the usual 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. The 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 to complete the crystalline orientation of the substrate film. The film was then wound into a roll to obtain a roll of release film (25 μm thick) having a release layer as shown in Table 2. The release film was unwound from the resulting release film roll and cut into A4 size samples, and the evaluations listed in Table 2 were performed. The amount of the aqueous coating composition applied was such that the thickness of the release layer after curing and stretching would be as shown in Table 2.

[0185] <Examples 2 to 8> A release film was obtained in the same manner as in Example 1, except that the aqueous coating composition obtained in the production example shown in Table 2 was used.

[0186] <Comparative Examples 1 and 2> A release film was obtained in the same manner as in Example 1, except that the aqueous coating composition obtained in the production example shown in Table 2 was used.

[0187] As shown in Table 2, in Examples 1 to 8, release films were obtained that were excellent in the coating uniformity of the release layer, immediate adhesion to the substrate, and releasability of the ceramic sheet. In contrast, in Comparative Example 1, the release layer was formed using an aqueous coating composition that did not contain a silicone having a (c) Q unit, so the crosslink density of the release layer was insufficient and the releasability was poor. Furthermore, immediate adhesion to the substrate was poor. In Comparative Example 2, the release layer was formed using an aqueous coating composition that did not contain an adhesion promoter, so immediate adhesion to the substrate was poor, and the release layer was transferred to the roll during the release film manufacturing process and to the back surface of the release film when the release film roll was wound up. This resulted in defects in the release layer, making it impossible to peel off the ceramic sheet.

[0188] [Table 2] [Industrial Applicability]

[0189] The release film of the present invention has a release layer with high peelability and wettability, and the adhesion between the substrate film and the release layer, particularly the immediate adhesion to the substrate, is high, and the release layer is less likely to fall off, so that the occurrence of defects can be suppressed when molding a thin resin sheet, particularly a ceramic green sheet.

Claims

1. A release film having a release layer on at least one surface of a polyester film, The release layer is a layer formed by reacting and solidifying an aqueous coating composition, The aqueous coating composition contains a silicone emulsion containing the following resin: A release film, wherein the aqueous coating composition further comprises a substrate adhesion promoter: (a) a first resin having a siloxane structure represented by Structural Formula 1; 【Chemistry 1】 (In Structural Formula 1, R1 is an alkenyl group having 2 to 8 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 8 carbon atoms, and k is 1 to 50.) (b) a second resin containing a hydrogen group; and SiO ４／２ (c) a third resin containing a silicone having Q units represented by the formula:

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

3. The (a) first resin and / or the (b) second resin further have a siloxane structure represented by the following structural formula 2: 【Chemistry 2】 2. The release film according to claim 1, wherein in structural formula 2, R3 is an alkyl group having 1 to 4 carbon atoms, Ar is an aryl group, and m is 1 or more and 50 or less.

4. 2. The release film according to claim 1, wherein the second resin (b) has a structure represented by the following chemical formula 2: 【Transformation 3】 (In Chemical Formula 2, l is 1 or more and 50 or less, m is 1 or more and 50 or less, and n is 0 or more and 5 or less)

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

6. 2. The release film according to claim 1, wherein the release film is a release film for use in producing a ceramic capacitor or a resin sheet.

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