Mold release film

Abstract

Provided is a mold release film that makes it possible to reduce the amount of an organic solvent, exhibits both good wettability and light releasability with respect to thin ceramic green sheets, and further exhibits superior adhesion between a release layer and a base material film. The present invention is a release film having a release layer on at least one surface of a polyester film, wherein: an aqueous coating composition for forming the release layer includes a silicone emulsion; the silicon emulsion contains (a) a first resin having a siloxane structure represented by the formula (R2-SiO-R1)k (in the formula, R1 is an alkenyl group having 2-8 carbon atoms, R2 is an alkyl group having 1-4 carbon atoms or an alkenyl group having 2-8 carbon atoms, and k is 1-50), (b) a second resin containing a hydrogen moiety, and (c) a silicone having a Q unit represented by the formula SiO4 / 2; and the first resin and / or the second resin further has a siloxane structure represented by the formula (R3-SiO-Ar)m (in structural formula 2, R3 is an alkyl group having 1-4 carbon atoms, Ar is an aryl group, and m is 1-50).

Description

Release film

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

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

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

[0004] Patent Documents 1 and 2 propose release films produced by a method (hereinafter referred to as "off-line coating") in which a coating composition containing a polysiloxane having an unsaturated group, a polysiloxane having 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"). Patent Document 4 proposes a release film in which a release layer is formed by offline coating using a coating composition containing an aryl group-containing silicone. Patent Document 5 further proposes a release film in which a release layer is formed by in-line coating using a coating composition containing a silicone having a Q unit.

[0006] Japanese Patent Application Laid-Open No. 2003-292894 International Publication No. WO2017 / 200056 Japanese Patent No. 5735278 Japanese Patent No. 5756315 Japanese Patent Application Laid-Open No. 2021-11081

[0007] 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.

[0008] In Patent Documents 1 and 2, the releasability and wettability of the thin ceramic green sheet are particularly insufficient, and there is a need for a better balance between easy releasability and good wettability. Furthermore, since a coating composition containing an organic solvent as a main component is used, there are problems with the adverse effects on the human body due to contact with the organic solvent or inhalation of its vapor, and with the burden on the global environment due to the release of organic solvent vapor into the atmosphere. Furthermore, the drying equipment for the organic solvent needs to be explosion-proof, which requires initial installation costs, and requires a large amount of energy to operate, so that CO ２ The problem was that the amount of emissions was large and the environmental impact was significant.

[0009] The release film described in Patent Document 3 has a release layer formed by in-line coating, but is not intended for use in molding ceramic green sheets, and has had problems with the releasability of thin ceramic green sheets in particular. Furthermore, a phenyl group-containing crosslinking agent is used to improve the adhesion between the substrate and the release layer, but the effect of the phenyl group on the release force has not been recognized, and the film is unsuitable as a release film that exhibits easy releasability.

[0010] 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 has problems with adverse effects on the human body and a large environmental load during the manufacturing process. Furthermore, because it 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 is cured at 135°C as described in the examples, the amount of heat required for curing the release layer is insufficient, which may adversely affect releasability. To further promote the curing of the release layer, it is 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.

[0011] The release film described in Patent Document 5 has a release layer that combines releasability and wettability formed by in-line coating. 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 a resin sheet, for example, a ceramic green sheet.

[0012] 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 between a base film and a release layer.

[0013] 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.

[0014] That is, the present invention has the following configuration: [1] A release film having a release layer on at least one surface of a polyester film, the release layer being a layer formed by reacting and solidifying an aqueous coating composition, the aqueous coating composition containing a silicone emulsion containing the following resin: (a) a first resin having a siloxane structure represented by Structural Formula 1;

[0015] (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 having a siloxane bond in its main chain and containing a hydrogen group, and SiO ４／２(c) a third resin containing a silicone having a Q unit represented by the following structural formula 2, wherein the first resin and / or the second resin further has a siloxane structure represented by the following structural formula 2:

[0016] (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.) [2] A release film according to [1], wherein the silicone emulsion contained in the aqueous coating composition further contains a (d) fourth resin having alkenyl groups only at the molecular terminals, and the (d) fourth resin has a number average molecular weight of 1,000 or more and less than 10,000. [3] The release film according to [1] or [2], wherein the (b) second resin has a structure represented by the following chemical formula 2:

[0017] (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.) [4] The release film according to any one of [1] to [3], wherein (a) the number average molecular weight of the first resin is 1,000 or more and less than 30,000, and (b) the number average molecular weight of the second resin is 1,000 or more and less than 5,000. [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 completion of crystal orientation, stretching the substrate film in at least one direction, and then heat-treating the substrate film to complete the crystal orientation of the substrate film. [6] The release film according to any one of [1] to [5], wherein the polyester film has a surface layer that is substantially free of inorganic particles, and the release layer is formed on the surface layer. [7] The release film according to any one of [1] to [6], wherein the release film is a release film for producing a ceramic capacitor or a resin sheet.

[0018] The release film of the present invention can improve the releasability and wettability of the release layer, and can further suppress the occurrence of defects in thin resin sheets, particularly ceramic green sheets. Furthermore, it can reduce harmful effects on the human body and environmental load during the production process. Furthermore, it is possible to form a release layer that does not have the risk of deteriorating the adhesion between the substrate film and the release layer.

[0019] The present invention has the characteristics described in this specification, and therefore can further solve the problems described below and achieve the effects. In particular, it is possible to further achieve both easy releasability and good wettability of the thin-layer ceramic green sheet. Furthermore, compared to coating compositions containing organic solvents as a main component, it is possible to significantly reduce the amount of organic solvent, or to make it substantially free of organic solvents. As a result, it is possible to significantly reduce the adverse effects on the human body caused by contact with organic solvents or inhalation of their vapors, and the burden on the global environment caused by the release of organic solvent vapors into the atmosphere. Furthermore, there is no need to use explosion-proof equipment for drying the organic solvent, and energy consumption during operation can be reduced compared to conventional manufacturing equipment. As a result, CO ２ It also reduces emissions and reduces the burden on the environment.

[0020] 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 obtain a release film with improved light releasability and also excellent substrate adhesion.

[0021] The present invention is described in detail below. The present invention relates to a release film having a release layer on at least one side of a polyester film, the release layer being a layer formed by reacting and solidifying an aqueous coating composition, the aqueous coating composition containing a silicone emulsion, and the silicone emulsion containing: (a) a first resin having a siloxane structure represented by Structural Formula 1;

[0022] (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 having a siloxane bond in its main chain and containing a hydrogen group, and (c) SiO４／２ (c) a third resin containing a silicone having a Q unit represented by the following structural formula 2:

[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.)

[0024] The present invention having such a configuration can achieve both easy releasability and good wettability of the release layer, and can provide a thin resin sheet, such as a thin ceramic green sheet, with a uniform thickness without defects and suppress defects such as pinholes. Furthermore, the present invention can achieve the following effects. The present invention uses an aqueous coating composition that contains significantly less organic solvent than conventional coating compositions, or an aqueous coating composition that is substantially free of organic solvents, which is less harmful to the human body and less burdensome to the environment, and reduces CO ２ It is possible to produce a release film while suppressing the occurrence of

[0025] 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 has excellent releasability, wettability, and substrate adhesion. More specifically, the inclusion of a silicone emulsion containing a silicone having Q units allows for a structure in which siloxane bonds are extended three-dimensionally. Therefore, a crosslinking reaction between the alkenyl group in the silicone molecule having Q units and the silicone having a hydrogen group progresses, 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, resulting in a release layer with excellent wettability. Furthermore, the inclusion of a silicone emulsion containing a silicone containing a siloxane structure having an aryl group allows for improved adhesion between the substrate film and the aryl group in the release layer due to intermolecular interactions between the substrate 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 substrate film is stretched after application of the coating composition, and can proceed when the crystal orientation after stretching is complete. By preventing the curing reaction from progressing when the substrate film is stretched, the stress generated by the difference between the stretchability of the substrate film and the stretchability of the coating composition can be reduced, preventing a decrease in substrate adhesion. In particular, in the present invention, the above-mentioned effect can be more effectively achieved by including a first resin, a second resin, and a third resin. In the present invention, the reaction delay effect of the aryl group can improve the substrate adhesion of the release layer. For example, in order to improve the substrate adhesion of the release layer, it is preferable that the curing reaction proceeds after stretching the substrate film. Here, as will be described later, it is difficult to structurally identify the orientation state and distribution of the resin component in the release layer, or the distribution of substituents that contribute to releasability on the surface of the release layer, and it has been discovered that in the present invention, "it is preferable that the curing reaction proceeds after stretching the substrate film."

[0026] (Polyester Film) The polyester constituting the polyester film used as the base film is not particularly limited, and a film formed from a polyester commonly used as a base material for release films can be used. Preferred are crystalline linear saturated polyesters composed of an aromatic dibasic acid component and a diol component. For example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or copolymers primarily composed of these resin components are even more preferred. Polyester films formed from polyethylene terephthalate are particularly preferred. The polyethylene terephthalate preferably contains 90 mol% or more, more preferably 95 mol% or more, of ethylene terephthalate repeating units, and may be copolymerized with small amounts of other dicarboxylic acid components or diol components. For example, from the standpoint of cost, polyethylene terephthalate produced solely from terephthalic acid and ethylene glycol is preferred. Furthermore, known additives, such as antioxidants, light stabilizers, UV absorbers, and crystallization agents, may be added within limits that do not impair the effects of the release film of the present invention. The polyester film is preferably a biaxially oriented polyester film due to its high bidirectional elastic modulus.

[0027] The intrinsic viscosity of the polyester film is preferably 0.50 dl / g or more and 0.70 dl / g or less, more preferably 0.52 dl / g or more and 0.62 dl / g or less. When the intrinsic viscosity is 0.50 dl / g or more, breakage does not occur frequently during the stretching process, which is preferable. Conversely, when the intrinsic viscosity is 0.70 dl / g or less, cuttability is good when cutting to a predetermined product width, and dimensional defects do not occur, which is preferable. It is also preferable to thoroughly vacuum dry the raw material pellets.

[0028] 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.

[0029] 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.

[0030] In the present invention, the stretching temperature during stretching of the polyester film is preferably equal to or higher than the second-order transition temperature (Tg) of the polyester. Stretching is preferably performed at a magnification of 1 to 8 times, particularly 2 to 6 times, in both the longitudinal and transverse directions.

[0031] The polyester film preferably has a thickness of 12 μm or more and 50 μm or less, more preferably 15 μm or more and 38 μm or less, and even more preferably 19 μm or more and 33 μm or less. A film thickness of 12 μm or more is preferable because there is no risk of deformation due to heat during film production, processing, or molding. On the other hand, a film thickness of 50 μm or less is preferable because the amount of film discarded after use is not excessively large, thereby reducing the environmental load.

[0032] 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.

[0033] In this embodiment, particles having a particle size of less than 1.0 μm and 1 nm or more may be present in the surface layer A. When the surface layer A is substantially free of particles having a particle size of 1.0 μm or more, such as inorganic particles, it is possible to reduce defects caused by the shape of particles in the substrate being transferred to the resin sheet.

[0034] In one embodiment, the surface layer A does not contain particles with a particle size of less than 1.0 μm, thereby more effectively preventing defects caused by the transfer of particle shapes in the substrate to the resin sheet. In one embodiment, the polyester film substrate is preferably a laminate film having a surface layer A that does not substantially contain inorganic particles on at least one side. This more effectively prevents defects caused by the transfer of particle shapes in the substrate to the resin sheet. For example, a preferred embodiment is that the surface layer A that does not substantially contain particles with a particle size of less than 1.0 μm also does not substantially contain particles with a particle size of 1.0 μm or more.

[0035] 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.

[0036] 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.

[0037] As for the laminate structure, if the layer on the side to which the release layer is applied is layer A, the layer on the opposite side is layer B, and the other core layer is layer C, the layer structure in the thickness direction can be a laminate structure such as release layer / A / B or release layer / A / C / B. Naturally, layer C may have a multi-layer structure. Furthermore, surface layer B may not contain inorganic particles. In that case, it is preferable to provide a coating layer containing inorganic particles and a binder on surface layer B to impart slip properties for winding the film into a roll.

[0038] In the polyester film substrate of the present invention, the surface layer B, which forms the surface opposite to the surface to which the release layer is applied, preferably contains inorganic particles, and in particular, silica particles and / or calcium carbonate particles, from the viewpoint of the slipperiness of the film and ease of air escape. The content of the inorganic particles contained in the surface layer B is preferably 5,000 ppm or more and 15,000 ppm or less in total.

[0039] In this case, the area surface average roughness (Sa) of the film of the surface layer B is preferably in the range of 1 nm to 40 nm. More preferably, it is in the range of 5 nm to 35 nm. When the total content of silica particles and / or calcium carbonate particles is 5,000 ppm or more and Sa is 1 nm or more, air can be uniformly released when the film is wound into a roll, resulting in a good wound shape and good flatness, making it suitable for producing ultrathin ceramic green sheets. Furthermore, when the total content of silica particles and / or calcium carbonate particles is 15,000 ppm or less and Sa is 40 nm or less, the lubricant is less likely to aggregate and large protrusions are not formed, which is preferable because it ensures stable quality when producing ultrathin ceramic green sheets.

[0040] In addition to silica and / or calcium carbonate, inactive inorganic particles and / or heat-resistant organic particles can also be used as particles contained in Layer B. However, from the viewpoints of transparency and cost, it is more preferable to use silica particles and / or calcium carbonate particles. Other inorganic particles that can be used include alumina-silica composite oxide particles and hydroxyapatite particles. Heat-resistant organic particles include crosslinked polyacrylic particles, crosslinked polystyrene particles, and benzoguanamine particles. When silica particles are used, porous colloidal silica is preferred, and when calcium carbonate particles are used, light calcium carbonate that has been surface-treated with a polyacrylic acid-based polymer compound is preferred from the viewpoint of preventing the lubricant from falling off.

[0041] The average particle size of the inorganic particles added to the surface layer B is preferably 0.1 μm or more and 2.0 μm or less, particularly preferably 0.5 μm or more and 1.0 μm or less. If the average particle size of the inorganic particles is 0.1 μm or more, the slipperiness of the release film is good, which is preferable. Furthermore, if the average particle size is 2.0 μm or less, there is no risk of adversely affecting the smoothness of the release layer surface, and there is no risk of pinholes occurring in the ceramic green sheet, which is preferable.

[0042] From the viewpoint of reducing pinholes, it is preferable that recycled raw materials or the like are not used for the surface layer A, which is the layer on which the release layer is to be formed, in order to prevent the inclusion of inorganic particles such as lubricants.

[0043] The thickness ratio of the surface layer A, which is the layer on which the release layer is provided, is preferably 20% to 50% of the total layer thickness of the base film. If it is 20% or more, the film is less likely to be affected from the inside by particles contained in the surface layer B, etc., and it is easy for the regional surface average roughness Sa to satisfy the above range, which is preferable. If it is 50% or less of the total layer thickness of the base film, the proportion of recycled raw materials used in the surface layer B can be increased, which is preferable as it reduces the environmental load.

[0044] From the viewpoint of economic efficiency, recycled raw materials such as film scraps and PET bottles may be used in an amount of 50% by mass to 90% by mass for the layers (surface layer B or the aforementioned intermediate layer C) other than the surface layer A. Even in this case, it is preferable that the type and amount of the lubricant contained in layer B, its particle size, and the area surface average roughness (Sa) satisfy the above-mentioned ranges.

[0045] Furthermore, in order to improve the adhesion of a release layer or the like to be applied later, or to prevent static charging, a coating layer may be provided on the surface of the surface layer A and / or the surface layer B before stretching or after uniaxial stretching in the film-forming process, or a surface treatment may be applied.

[0046] In one embodiment, the release layer-forming surface to which the aqueous coating composition is applied can be subjected to a surface treatment or provided with an easy-adhesion layer in order to enhance adhesion to the release layer. Examples of surface treatments include plasma treatment, corona discharge treatment, ultraviolet treatment, flame treatment, and electron beam / radiation treatment. Examples of the easy-adhesion layer include a layer containing the same resin as the substrate film and further containing an antistatic agent, a pigment, a surfactant, a lubricant, an antiblocking agent, etc. When an adhesion improver such as a coupling agent is added to the aqueous coating composition, the release layer can have sufficient adhesion to the substrate film even without providing an easy-adhesion layer, etc.

[0047] (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 the silicone emulsion contains the following: (a) a first resin having a siloxane structure represented by Structural Formula 1;

[0048] (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 having a siloxane bond in its main chain and containing a hydrogen group; (c) SiO ４／２ wherein the first resin and / or the second resin further has a siloxane structure represented by the following structural formula 2:

[0049] (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.)

[0050] 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 the resin sheet or ceramic green sheet, and can form a sheet with a uniform thickness. In addition, a release layer with excellent adhesion to the substrate 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.

[0051] 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, also contains (d) a fourth resin. 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. Furthermore, 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, all of (a), (b), (c), and (d) may be contained in a single silicone emulsion.

[0052] The aqueous coating composition preferably does not substantially contain organic solvent, and uses water as a dispersion medium.By substantially not containing organic solvent, the stability of silicone emulsion is improved, and it can prevent the composition change of the aqueous coating composition due to emulsion destruction, and the aggregation and gelation of the resin in the silicone emulsion.The meaning of substantially not containing organic solvent means, for example, that the content is 10000 ppm or less, preferably 5000 ppm or less, more preferably 3000 ppm or less, and most preferably below the detection limit per total weight of the aqueous coating composition.This is because, even if organic solvent is not intentionally used, a small amount of organic solvent used in the polymerization process of the resin contained in the silicone emulsion or the emulsification process of the emulsion may remain.

[0053] (a) First Resin The (a) first resin contained in the silicone emulsion preferably has the following structure:

[0054] (In Structural Formula 1, R1 is an alkenyl group having from 2 to 8 carbon atoms, R2 is an alkyl group having from 1 to 4 carbon atoms or an alkenyl group having from 2 to 8 carbon atoms, and k is from 1 to 50.) By having Structural Formula 1, a crosslinking reaction between the alkenyl group and the silicone having a hydrogen group progresses, resulting in a release layer with high crosslink density, excellent solvent resistance, and easy releasability. Examples of alkenyl groups include vinyl groups, allyl groups, butenyl groups, pentenyl groups, and hexenyl groups, and of these, vinyl groups are particularly preferred.

[0055] (a) The first resin may have a structure represented by the following chemical formula 1, for example.

[0056] In the above chemical formula 1, R1 is an alkenyl group having 2 to 8 carbon atoms, and R2 is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 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. 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 also preferred. k is a structure that contributes to the crosslinking reaction and is preferably 1 to 50. o is a structure that contributes to releasability and is preferably 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.

[0057] As illustrated in Chemical Formula 1, SiO ２／２From the viewpoint of releasability, it is preferable that the silicone be 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 arranged on the outside of the molecular chain, so that the silicone exhibits hydrophobicity and forms a release layer with excellent releasability, which is preferable.

[0058] In one embodiment, the first resin contained in the silicone emulsion preferably further has the following structural formula 2:

[0059] (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 having an aryl group, which is a bulky substituent as in Structural Formula 2, the curing reaction of the release layer is delayed, and curing of the release layer is completed when crystal orientation is completed after the substrate film is stretched. Since the curing reaction is delayed and curing of the release layer does not progress easily when the substrate film is stretched, the stretchability of the coating composition is maintained, and there is no risk of a decrease in adhesion due to a stress difference between the substrate film and the release layer, which is preferable. In addition, the obtained release layer is free of defects such as coating film cracking that occur during stretching, and has excellent releasability, which is preferable.

[0060] 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 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.

[0061] 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.

[0062] 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 integral ratio is calculated from the integral ratio of the peaks derived from each siloxane structure.

[0063] 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 and the risk of heavy releasability. The amount of silicone emulsion in the aqueous coating composition can be appropriately adjusted so that the first resin falls within the above range. In the present invention, the total solids content in the coating composition refers to the sum of the solids content of the first resin, second resin, third resin, and a fourth resin added as needed.

[0064] (b) Second Resin) The second resin (b) having a siloxane bond in its main chain and containing a hydrogen group may be any compound having a siloxane bond in its main chain, but is preferably a polyorganosiloxane having a hydrogen group at its terminal 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, and exhibits easy releasability.

[0065] In one embodiment, the second resin has a structure represented by the following Chemical Formula 2.

[0066] 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. When l is 1 or more and 50 or less, the crosslinking reaction between the alkenyl group and the hydrogen group in the coating composition proceeds, resulting in a release layer with high crosslink density and excellent solvent resistance, which is preferable. When m is 1 or more and 50 or less, the bulky phenyl group causes a reaction delay during curing of the release layer, resulting in a release layer with good stretchability and excellent adhesion, which is preferable. Furthermore, the π electrons of the phenyl group interact with the substrate film, resulting in even better adhesion, which is preferable. When n is 0 or more and 5 or less, the compatibility with the (a) first resin or the (d) fourth resin described below in the coating composition decreases, which makes it easier for the (a) first resin or the (d) fourth resin to localize on the surface side of the release layer, which is preferable. As a result, a release layer with excellent releasability is obtained, which is preferable.

[0067] 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 integral ratio is calculated from the integral ratio of the peaks derived from each siloxane structure.

[0068] 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 the amount of unreacted components increases and there is no risk of heavy peeling. The amount of silicone emulsion in the aqueous coating composition can be appropriately adjusted so that the content of the second resin falls within the above range. For example, when the (b) second resin contains an aryl group represented by Structural Formula 2, when the total solid content of the coating composition is taken as 100, 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. By satisfying these conditions, the crosslinking reaction proceeds sufficiently, and there is no risk of unreacted components increasing and causing heavy peeling, which is preferable.

[0069] 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 presumed 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), making it easier for the second resin (a) to localize on the surface side 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, and adhesion is also improved by increasing the interaction between the substrate film and the release layer. Thus, the present invention can solve the conventional problems of excessively delayed curing reactions, such as the need for a long time for curing the release layer, and the inability to obtain the desired release layer due to the rapid progress of the curing reaction. In another embodiment, the structure containing the aryl group represented by Structural Formula 2 may be present in both the first resin (a) and the second resin (b).

[0070] (c) Third Resin The silicone emulsion in the aqueous coating composition of the present invention contains SiO ４／２ It is preferable to contain 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 silicone having the structure dispersed in water as 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. In addition, 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.

[0071] SiO ４／２ Examples of silicones having a Q unit represented by the formula R4 include those having a structure represented by the following formula 3: 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 between 0 and 3, and b is an integer between 0 and 3, and a + b ≦ 3.) Here, Chemical Formula 3 represents a general formula, and a structural unit where a = 0 and b = 0 is a Q unit, and (c) the third resin has this Q unit. Furthermore, a structural unit where a = 1 or a = 2 is a siloxane structure having an alkenyl group, and a 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, a structural unit where a + b = 3 represents a siloxane structure having a terminal group.

[0072] Examples of alkenyl groups having 2 to 8 carbon atoms represented by R4 include vinyl groups, allyl groups, butenyl groups, pentenyl groups, and hexenyl groups, with vinyl groups being particularly preferred. Examples of alkyl groups represented by R5 include methyl groups, ethyl groups, propyl groups, and butyl groups, and examples of aryl groups include phenyl groups and tolyl groups. It is preferable that an alkenyl group having 2 to 8 carbon atoms represented by R4 is included in (c) from the viewpoint of reactivity with hydrogen groups, and the fewer carbon atoms there are, the less the influence of steric hindrance there is 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.

[0073] Silicone having Q units can have a structure in which the siloxane bond is expanded three-dimensionally, and therefore the alkenyl group in the molecule can also be spread three-dimensionally. Therefore, a dense crosslinked structure can be formed by the reaction of the (b) second resin, which is silicone having a hydrogen group, with the alkenyl group in the (c) molecule, and a release layer with excellent solvent resistance can be obtained. Generally, SiO contained in the release layer ２／２As the ratio of D units represented by the formula (2) 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, resulting in hydrophobicity. 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, resulting in reduced hydrophobicity. Without being limited by any particular theory, by using a release layer containing silicone having 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.

[0074] 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 in the coating composition is taken as 100. When it is 10% by mass or more, the silicone having Q units breaks the helical structure of the silicone consisting of D units contained in the release layer, which is preferable, and when it is 70 parts by mass or less, the silicone having Q units does not break the helical structure of the silicone consisting of D units contained in the release layer too much, which is preferable, and a release layer with excellent releasability is obtained.

[0075] The content of Si atoms contained in the Q unit is SiO ４／２ The 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 %. When the content of Si atoms in the Q units is 0.05 mol % or more, the siloxane bonds can assume a structure in which they are sufficiently extended three-dimensionally, and the effect of increasing the crosslink density is exhibited, which is preferable. When the content is 60 mol % or less, excessive wettability is not imparted, and there is no risk of severe peeling, which is preferable. Furthermore, from the viewpoint of forming a dense crosslinked structure by reaction with (b) the second resin, the content of Si atoms in the siloxane structure having an alkenyl group is SiO ４／２It is preferably 0.05 to 30 mol %, more preferably 1.0 to 20 mol %, based on all Si atoms in the silicone having Q units represented by the formula:

[0076] 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 is therefore a release layer that exhibits easy peelability, which is preferable.

[0077] As mentioned above, silicones having Q units have a rigid molecular skeleton and therefore poor stretchability, which may cause coating film cracking and 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 silicones having Q units can be formed without poor adhesion or coating defects.

[0078] (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.

[0079] (d) Examples of the fourth resin include those shown in Chemical Formula 4 below.

[0080] 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. Having p within the above range is preferable because it exhibits excellent releasability. Since the (d) fourth resin has alkenyl groups only at both ends, the D units are connected in a linear chain, and the helical structure is not disrupted by crosslinking reactions, resulting in superior releasability compared to the (a) first resin. However, in an embodiment including a fourth resin having alkenyl groups only at the molecular ends, the amount of alkenyl groups is less than that of the (a) first resin, which may result in a decrease in crosslink density. However, at the same time, the crosslinking reaction between the silicone (a) first resin, which has alkenyl groups in its side chain and is present in the release layer, can prevent a deterioration in solvent resistance. Although not limited by any particular theory, the release film of the present invention has a fourth resin, silicone (d) having alkenyl groups only at both ends, localized on the surface of the release layer, and is bonded to a silicone (c) having a Q unit and an alkenyl group via a first resin (a) having an alkenyl group in the side chain, thereby forming a release layer having excellent releasability.

[0081] 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 integral ratio is calculated from the integral ratio of the peaks derived from each siloxane structure.

[0082] 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. When it is 1% by mass or more, it is preferable because it can be localized on the surface of the release layer and exhibit releasability. When it is 50% by mass or less, the crosslink density of the release layer decreases, which is preferable because there is no risk of heavy releasability. The amount of silicone emulsion in the aqueous coating composition can be appropriately adjusted so that the fourth resin is within the above range.

[0083] (Other Components) The aqueous coating composition of the present invention preferably contains a surfactant. By containing a surfactant, excellent coatability is achieved when the coating composition is applied to a polyester film, which is a substrate film, and there is no risk of coating defects such as repelling, which is preferable. In addition, 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 preferable because it can suppress the occurrence of unevenness in the release layer and coating unevenness.

[0084] The aqueous coating composition of the present invention must contain a platinum-based catalyst to allow the addition reaction between the silicone having an alkenyl group and the silicone having a hydrogen group. Known platinum-based catalysts can be used, such as platinum chloride and chloroplatinic acid. Taking into account dispersibility in silicone, the platinum-based catalyst may be a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt's catalyst). Uniform dispersion can be ensured by simultaneously dispersing the silicone during emulsification.

[0085] 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 risk of silicone aggregates being generated. The amount of platinum catalyst is more preferably 600 ppm or less, even more preferably 500 ppm or less, and even more preferably 300 ppm or less. Furthermore, an amount of 10 ppm or more is preferable because the silicone addition reaction proceeds efficiently, resulting in sufficient curing of the release layer and exhibiting light releasability.

[0086] 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 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 it sufficiently suppresses the activity of the platinum-based catalyst. 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.

[0087] The aqueous coating composition of the present invention may further contain an adhesion promoter, a colorant, an ultraviolet absorber, particles, etc., within the scope of the invention.

[0088] (Other Features of the Release Layer) The film thickness of the release layer in the present invention is preferably 0.001 to 0.2 μm, more preferably 0.005 to 0.1 μm, after drying and curing. 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 excellent coatability can be obtained when applied to a substrate film.

[0089] (Method for producing a release film) In one embodiment, a release layer is formed on at least one surface of a substrate film. The release layer is formed by applying an aqueous coating composition to the substrate film, followed by heat drying, and then reacting and solidifying the components in the aqueous coating composition. The release layer is preferably formed during the film formation process.

[0090] When applying an aqueous coating composition to a substrate film, the solids concentration is preferably 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less, based on the components in the aqueous coating composition, i.e., the solids. When the solids concentration of the release layer components in the aqueous coating composition is above the lower limit, the film-forming properties tend to be good. When the solids concentration is below the upper limit, the stability of the aqueous coating composition and the appearance of the release layer tend to be good. Water is preferably used as the aqueous solvent for adjusting the solids concentration.

[0091] 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.

[0092] Here, polyester films before the completion of crystal orientation include unstretched films, uniaxially oriented films obtained by orienting unstretched films in either the longitudinal direction (hereinafter sometimes referred to as the direction of continuous film production, longitudinal direction, or MD direction) or the transverse direction (hereinafter sometimes referred to as the direction perpendicular to the longitudinal direction, width direction, or TD direction), and also films that have been stretched and oriented at a low ratio in both the longitudinal and transverse directions (biaxially stretched films before they are finally re-stretched in the longitudinal or transverse direction to complete the orientation crystallization).

[0093] 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.

[0094] 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.

[0095] In the present invention, the aqueous coating composition forming the release layer is stretched longitudinally and / or transversely together with the applied film, and it is presumed that the first resin, second resin, third resin, and optionally the fourth resin contained in the silicone emulsion are oriented and interact with each other. For example, during the drying process of the water in the aqueous coating composition, during stretching of the substrate film, or during hardening of the release layer, it is presumed that the difference in compatibility or molecular weight between the first resin, second resin, and third resin makes (a) more likely to localize on the surface side of the release layer, thereby improving releasability. 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 also improves the adhesion between them. However, it is difficult to structurally identify the orientation and distribution of the resin components in the release layer, or the distribution of substituents and other elements that contribute to releasability on the surface of the release layer.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] (Resin Sheet) The resin sheet of the present invention is not particularly limited as long as it is a sheet molded onto 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 molded by melt casting or solution casting using an organic component with 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. 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.

[0100] (Ceramic Green Sheet and Ceramic Capacitor) Generally, a multilayer ceramic capacitor has a rectangular parallelepiped ceramic body. First internal electrodes and second internal electrodes are alternately provided inside the ceramic body along the thickness direction. The first internal electrodes are exposed at a first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrode is electrically connected to the first external electrode at the first end face. The second internal electrode is exposed at a second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrode is electrically connected to the second external electrode at the second end face.

[0101] In one aspect, the release film of the present invention is a release film for producing ceramic green sheets and is used to produce such multilayer ceramic capacitors. 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 then divided into multiple pieces to produce green ceramic bodies. The green ceramic bodies are then fired to obtain ceramic bodies. Then, first and second external electrodes are formed to complete a multilayer ceramic capacitor.

[0102] 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.

[0103] (Release Layer Thickness) The release film was cut into triangular pieces, and then a 2 nm thick Pt (platinum) layer was formed on the release layer surface by coating. The obtained sample was fixed in a multi-axis embedding capsule, embedded using epoxy resin, and sliced ​​in a direction perpendicular to the film surface using a microtome ULTRACUT-S to obtain an ultrathin sample with a height of 50 nm. The obtained ultrathin sample was then mounted on a grid and steam-stained with 2% osmic acid at 60 °C for 2 hours. Using the ultrathin sample after steam staining, the film cross section was observed using a transmission electron microscope LEM-2000 at an acceleration voltage of 100 kV, and the thickness of the release layer was measured. Measurements were performed at 10 random points, and the average value was taken as the thickness of the release layer.

[0104] (Coating Uniformity of Release Layer) The release film obtained by winding into a roll was unwound and cut into A4 size sheets, and the release layer surface was visually observed using a fluorescent lamp and a halogen light to compare the number of aggregated coating defects (number per A4 size sheet) and evaluate according to the following criteria: ◎: No coating defects ○: 1 to 2 coating defects △: 3 to 5 coating defects ×: 6 or more coating defects

[0105] (Adhesion to substrate) The release surface of the release film was rubbed with a thumb 10 times at a load of about 500 gf, and an adhesive tape (manufactured by Nitto Denko Corporation, product name "No. 31B tape") was stuck to the rubbed area to check for silicone detachment. The peeling state of the adhesive tape was checked and evaluated according to the following criteria: ○: No change in peeling when the adhesive tape was peeled △: Slight change in peeling when the adhesive tape was peeled ×: Change in peeling when the adhesive tape was peeled

[0106] (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 left to stand for 30 seconds. Similarly, the static contact angles of ethylene glycol and methylene iodide were 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 (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 total value of each surface tension component in 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 + cos θ3) / 2 Note that γLD, γLP, γLH, and γL for water, ethylene glycol, and methylene iodide are as shown in Table 1.

[0107] 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

[0108] (Ceramic Sheet Removability) A slurry composition I consisting of the following materials was mixed by stirring for 10 minutes and dispersed with zirconia beads having a diameter of 0.5 mm using a bead mill for 10 minutes to obtain a primary dispersion. Then, a slurry composition II consisting of the following materials was added to the primary dispersion so that the ratio of (slurry composition I):(slurry composition II) was 3.4:1.0, and a secondary dispersion was performed with zirconia beads having a diameter of 0.5 mm using a bead mill for 10 minutes to obtain a ceramic slurry. (Slurry composition I) Toluene 22.3 parts by mass Ethanol 18.3 parts by mass Barium titanate (average particle size 100 nm) 57.5 parts by mass Homogenol L-18 (Kao Corporation) 1.9 parts by mass (Slurry composition II) Toluene 39.6 parts by mass Ethanol 39.6 parts by mass Dioctyl phthalate 3.3 parts by mass Polyvinyl butyral (S-LEC BM-S, manufactured by Sekisui Chemical Co., Ltd.) 16.3 parts by mass 1-ethyl-3-methylimidazolium ethyl sulfate 0.5 parts by mass Next, the release surface of the obtained release film sample was coated using an applicator so that the slurry after drying would be 2.0 μm, and the coating was dried at 60 ° C. for 1 minute to obtain a release film with a ceramic green sheet. The resulting release film with ceramic green sheet was destaticized 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 speed 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 fixing the release film by adhering the release film side to the double-sided tape. The ceramic green sheet was then peeled by pulling the tape. Of the measured values, the average peel force for peel distances of 20 mm to 70 mm was calculated, and this value was used as the peel force. Measurements were performed five times, and the average peel force was used for evaluation. The obtained peel force values ​​were evaluated according to the following criteria.◎: Less than 1.0 mN / mm ◯: Less than 1.5 mN / mm △: Less than 2.0 mN / mm ×: 2.0 mN / mm or more.

[0109] (Silicone emulsion: a-1) Using an emulsifier capable of stirring the entire contents of a container (manufactured by N.P. Labo, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of alkenyl group-containing silicone represented by chemical formula (a-1) (o = 125, k = 4, number average molecular weight 9756) and 2% by mass of polyoxyethylene lauryl ether (manufactured by 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 adjusted by adjusting the stirring speed and stirring time during emulsification.

[0110]

[0111] (Silicone emulsion: a-2) Using an emulsifier capable of stirring the entire contents of a container (manufactured by N.P. Labo, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of alkenyl group- and phenyl group-containing silicone represented by chemical formula (a-2) (o = 115, k = 4, m = 5, number average molecular weight 9696) and 2% by mass of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain a silicone emulsion (a-2) with a solids content of 20% by mass. The emulsion particle size was adjusted by adjusting the stirring speed and stirring time during emulsification.

[0112]

[0113] (Silicone emulsion: b-1) Using an emulsifier capable of stirring the entire contents of a container (manufactured by N.P. Labo, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of hydrogen group- and phenyl group-containing silicone represented by chemical formula (b-1) (l = 21, m = 8, n = 4, number average molecular weight 2806) and 2% by mass of polyoxyethylene lauryl ether (manufactured by 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 adjusted by adjusting the stirring speed and stirring time during emulsification.

[0114]

[0115] (Silicone emulsion: b-2) Using an emulsifier capable of stirring the entire contents of a container (manufactured by N.P. Labo, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of hydrogen group- and phenyl group-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 (manufactured by 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 adjusted by adjusting the stirring speed and stirring time during emulsification.

[0116]

[0117] (Silicone emulsion: c-1) Using an emulsifying device capable of stirring the entire container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), SiO ４／２ A silicone emulsion (c-1) containing 98% by mass of a 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 a silicone having Q units. ４／２The silicone having the Q unit represented by the formula (3) is represented by the general formula, in which 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 all Si atoms in the silicone having Q units represented by the formula (3) was 5 mol %, and the content of Si atoms contained in Q units was 40 mol %. That is, in Chemical Formula 3, R4 was a vinyl group, R5 was a methyl group, and 5 mol % of the siloxane structure with a = 1, b = 1 was present, 40 mol % of the siloxane structure with a = 0, b = 0 was present, and 55 mol % of the siloxane structure with R5 being a methyl group, a = 0, b = 2 or 3 was present. 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. 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.)

[0118] (Silicone emulsion: d-1) Using an emulsifier capable of stirring the entire contents of a container (manufactured by N.P. Labo, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of silicone having alkenyl groups only at both ends and represented by chemical formula (d-1) (p=23, number average molecular weight 1888) and 2% by mass of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade 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 adjusted by adjusting the stirring speed and stirring time during emulsification.

[0119]

[0120] Aqueous Coating Composition Production Example 1 An aqueous coating composition was obtained by mixing silicone emulsion (a-1), silicone emulsion (b-1), silicone emulsion (c-1), silicone emulsion (d-1), and water in the proportions shown in Table 2 so that the solids concentration was 4% by mass. At this time, 0.02% by 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.

[0121] <Aqueous Coating Composition Production Examples 2 to 8> Aqueous coating compositions were 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.

[0122] Example 1 Polyethylene terephthalate ([η] = 0.63 dl / g, Tg = 78°C) containing 0.25% by mass of calcium carbonate particles with an average particle size of 0.6 μm was melted in an extruder, passed through a filter with a filtration accuracy of 10 μm, extruded from a die, and cooled on a cooling drum in a conventional manner to form an unstretched film. The polyester film was then stretched 3.2 times in the longitudinal direction at 80°C, and the aqueous coating composition obtained in Production Example 1 was uniformly applied to one surface of the polyester film using a roll coater. This coated film was then dried at 115°C, stretched 4.0 times in the transverse direction at 145°C, and further heat-set at 230°C for approximately 10 seconds to complete the crystalline orientation of the substrate film. The film was then wound into a roll to obtain a roll of release film (thickness 25 μm) having a release layer as shown in Table 2. The release film was unwound from the resulting release film roll and cut into an A4 size sample, and the evaluations described in Table 2 were performed using the samples. 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.

[0123] Examples 2 to 6 Release films were obtained in the same manner as in Example 1, except that the aqueous coating compositions obtained in the production examples shown in Table 2 were used.

[0124] Comparative Examples 1 and 2 Release films were obtained in the same manner as in Example 1, except that the aqueous coating compositions obtained in the production examples shown in Table 2 were used.

[0125] Reference Example 1 The aqueous coating composition obtained in Production Example 1 was applied to one surface of a 25 μm-thick biaxially stretched polyester film (Toyobo Ester Film E5100, manufactured by Toyobo Co., Ltd.) using reverse gravure so that the thickness of the release layer after drying would be 0.1 μm, and the film was dried at 135° C. for 60 seconds and then wound up into a roll to obtain a release film roll. The release film was unwound from the obtained release film roll, and the evaluations listed in Table 2 were carried out using a sample cut into an A4 size.

[0126] As shown in Table 2, Examples 1 to 6 produced release films with excellent release layer coating uniformity, substrate adhesion, and ceramic sheet releasability. Furthermore, the surface free energy of the release layer was 17 mN / m or greater, resulting in release films with excellent ceramic slurry wettability. 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, resulting in insufficient ceramic sheet releasability. In Comparative Example 2, the release layer was formed using an aqueous coating composition that did not contain a siloxane structure having an aryl group, resulting in poor stretchability of the coating composition and poor substrate adhesion. Furthermore, the ceramic sheet releasability was also poor. Meanwhile, in Reference Example 1, the release layer was formed using an offline coating method, resulting in insufficient heat for drying and curing the aqueous coating composition, resulting in deformation of the release layer when wound into a roll. As a result, the release layer coating uniformity, substrate adhesion, and ceramic sheet releasability were poor. Furthermore, the contact angle values ​​of the release layer varied significantly, making it difficult to accurately measure the surface free energy.

[0127]

[0128] The release film of the present invention has a release layer with high peelability and wettability, and has a high adhesion between the base film and the release layer, making the release layer less likely to fall off, thereby suppressing the occurrence of defects 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 being a layer formed by reacting and solidifying an aqueous coating composition, the aqueous coating composition containing a silicone emulsion including the following resins: (a) a first resin having a siloxane structure represented by structural formula 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 having a siloxane bond in the main chain and containing a hydrogen group, and SiO ４／２ (c) a third resin containing a silicone having a Q unit represented by the following structural formula 2: (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), a release film.

2. The release film according to claim 1, wherein the silicone emulsion contained in the aqueous coating composition further contains a fourth resin (d) having alkenyl groups only at the molecular ends, and the number average molecular weight of the fourth resin (d) is 1,000 or more and less than 10,000.

3. The release film according to claim 1, wherein the second resin (b) has a structure represented by the following chemical formula 2: (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.) 4. The release film according to claim 1, wherein the number average molecular weight of the first resin (a) is 1,000 or more and less than 30,000, and the number average molecular weight of the second resin (b) is 1,000 or more and less than 5,000.

5. The release film according to claim 1, wherein the release film is formed by applying the aqueous coating composition to a substrate film before 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 claim 1, wherein said polyester film has a surface layer that is substantially free of inorganic particles, and said release layer is formed on said surface layer.

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

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