Mold release film

Abstract

The present invention provides a mold release film that can achieve both peelability of a mold release layer formed from a water-based coating composition from a ceramic green sheet and close adhesion of the mold release layer to a substrate, and that exhibits good recyclability, where the surface of the mold release layer has excellent wettability with respect to ceramic slurry. This mold release film has a substrate film and a mold release layer formed by reacting and curing a water-based coating composition. The water-based coating composition contains: an alkenyl group-containing silicone (A); a Si-H group-containing silicone (B); and a silane coupling agent (C). When the total amount of (A), (B), and (C) is taken as 100 parts by mass, the content of (C) exceeds 15 parts by mass.

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 using a polyester film or the like as a substrate 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, as the release layer of a release film, many release layers formed from coating compositions containing silicone have been proposed because of their good heat resistance and releasability (Patent Documents 1 to 4).

[0003] Patent Document 1 describes a release film having an undercoat layer formed using a coating liquid containing an anionic antistatic agent and a silane coupling agent, and a release layer thereon using a curable silicone, and describes that the release layer has excellent curability, adhesion to a substrate film, and antistatic properties.

[0004] Patent Document 2 proposes a release film in which a release layer is formed from a composition containing polysiloxane having an unsaturated group, and a water-soluble silane coupling agent containing a succinic anhydride group, a quaternary ammonium group, a ureido group, etc. It is described as having the effect of providing adequate releasability for pressure-sensitive adhesives and exhibiting excellent adhesion to plastic film substrates.

[0005] Patent Document 3 proposes a release film coated with a coating agent consisting of a silicone resin containing a phenyl group, a silicone crosslinking agent, a silane coupling agent, a metal catalyst, and a solvent, and describes the film as having suitable release properties for polyurethane films used in paint protection films and the like.

[0006] Patent Document 4 proposes a release film having a release layer formed thereon that contains polysiloxane having an unsaturated group. It describes that by adjusting the molecular weight and the content of polysiloxane having an unsaturated group, the film has the effect of achieving good releasability from the adhesive and reducing migration of the adhesive to the substrate, regardless of the peeling speed during use.

[0007] JP 2014-233913 A JP 2020-70311 A JP 2021-510758 A WO2017 / 200056 A

[0008] One application of release films that has attracted attention is as a process film for molding ceramic green sheets, which require high smoothness for ceramic capacitors, ceramic substrates, etc. 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.

[0009] As a method for producing a release film, a method in which a release layer is applied to a substrate film during the stretching film formation (hereinafter referred to as "inline coating") has attracted attention. This method is environmentally friendly because it uses a water-based coating composition, can produce large quantities at one time, and can reduce costs because it can be produced in a single process, and is therefore considered to be a more useful production method than offline coating, which applies a solvent-based coating composition.

[0010] In recent years, as multilayer ceramic capacitors have become smaller and larger in capacity, the thickness of ceramic green sheets has tended to decrease, leading to a demand for ceramic green sheets with a thickness of 1.0 μm or less. While releasability is required for ceramic green sheets with a thickness of 1.0 μm or less, maintaining releasability requires adhesion between the release layer and the substrate film. Achieving both releasability and adhesion between the release layer and the substrate film has become difficult. In other words, adding a component such as an acrylic resin with a polarity similar to that of the substrate film to the release layer to improve adhesion between the release layer and the substrate film increases the polarity not only on the substrate film side but also on the surface side of the release layer, resulting in a problem of reduced releasability. Furthermore, as ceramic green sheets become thinner, uneven thickness of the release layer can easily repel the ceramic slurry applied during ceramic sheet production. Therefore, the release layer surface must be sufficiently wettable to allow for uniform application of the ceramic slurry. Furthermore, recyclability, which allows for reuse of the release film, is also required from cost and environmental perspectives. However, there have been no examples of release films that combine recyclability and adhesion between the release layer and the base film while also having recyclability and wettability of the release layer surface to ceramic slurries. For example, with regard to recyclability, when recycled resin made from a release film is used in a new release film, foreign matter from the recycled resin can be generated and appear as protrusions on the surface, deteriorating the surface smoothness. If the adhesion between the release layer and the base film is weak, the release layer comes into contact with the transport roll when the release film is transported, and the release layer is transferred to the transport roll, causing a problem of change in releasability during the ceramic slurry coating process.

[0011] Patent Documents 1 to 4 do not solve all of the above problems.

[0012] An object of the present invention is to provide a release film that can achieve both good releasability of a release layer made of an aqueous coating composition from a ceramic green sheet and good adhesion between the release layer and a substrate film, and also to provide a release film that has the advantages of good recyclability and excellent wettability of the release layer surface with a ceramic slurry.

[0013] As a result of extensive research into solving these problems, the present inventors discovered that the above problems could be solved by a release layer formed by reacting and solidifying an aqueous coating composition containing an alkenyl group-containing silicone (A), an Si—H group-containing silicone (B), and a predetermined amount of a silane coupling agent (C), and thus completed the present invention.

[0014] [1] A release film for forming a resin sheet, comprising a base film and a release layer formed by reacting and solidifying an aqueous coating composition, wherein the aqueous coating composition contains an alkenyl group-containing silicone (A), a Si—H group-containing silicone (B), and a silane coupling agent (C), and when the total amount of the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C) is taken as 100 parts by mass, the content of the silane coupling agent (C) is 15 parts by mass or more.

[0015] [2] The release film for forming a resin sheet according to [1], wherein the alkenyl group-containing silicone (A) has a number average molecular weight of 1,000 or more and less than 50,000.

[0016] [3] The release film for forming a resin sheet according to claim 1, wherein the alkenyl group-containing silicone (A) has a structure represented by general formula (I).

[0017]

[0018] (In general formula (I), R1 may be the same or different and is an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms, including an alkyl group or a phenyl group; [SiO] b1 Y1s bonded to silicon atoms represented by the formula (II) may be the same or different, and are each an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms containing an alkyl group or a phenyl group, or are represented by the formula (II), in which R1 may be the same group as at least one R1 in the formula (I), and in which R1s in the formula (II) may be the same or different.

[0019]

[0020] [4] The release film for forming a resin sheet according to any one of [1] to [3], wherein the content of the Si—H group-containing silicone (B) is 20 parts by mass or less when the total amount of the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C) is taken as 100 parts by mass.

[0021] [5] The release film for forming a resin sheet according to any one of [1] to [4], wherein the number average molecular weight of the Si—H group-containing silicone (B) is 1,000 or more and less than 50,000.

[0022] [6] The release film for forming a resin sheet according to any one of [1] to [5], wherein the silane coupling agent (C) has at least one functional group selected from 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, and a carboxyl group.

[0023] [7] The release film for forming a resin sheet according to any one of [1] to [6], wherein the aqueous coating composition further contains a wettability improver.

[0024] [8] The release layer 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. [1] The release film for forming a resin sheet according to any one of [1] to [7].

[0025] [9] The release film for forming a resin sheet according to any one of [1] to [8], wherein the base film is a polyester film.

[0026]

[10] The release film for a resin sheet according to any one of [1] to [9], wherein the resin sheet is a ceramic green sheet.

[0027] According to the present invention, it is possible to provide a release film for forming a resin sheet, which has the advantages of easily achieving both the releasability of the release layer and the adhesion between the substrate and the release layer, and further has good recyclability and excellent wettability with a ceramic slurry.

[0028] Although the details of why this effect is achieved are unclear, it is thought that the arrangement of silicone on the surface side of the release layer exhibits releasability, and the reaction of the silane coupling agent on the base film side improves adhesion between the release layer and the base film. The presence of the silane coupling agent on the base film side makes the surface side of the release layer rich in silicone components, achieving both releasability and adhesion between the release layer and the base film. Furthermore, the reaction of the silane coupling agent results in a hard release layer that is less likely to deform during peeling, which is thought to result in even better releasability.

[0029] Furthermore, the present invention can exhibit good adhesion between the release layer and the substrate film and good releasability from resin sheets such as green sheets, and can exhibit good releasability even from green sheets with a thickness of 1.0 μm. Therefore, the present invention can be applied to the recent demand for thinner resin sheets such as ceramic green sheets.

[0030] To apply this technology to thinner resin sheets such as ceramic green sheets and maintain peelability, adhesion between the release layer and the base film is necessary. However, it is becoming increasingly difficult to achieve both peel strength and adhesion between the release layer and the base film.

[0031] In contrast, by ensuring that the blending amounts of the resin component and the silane coupling agent (C) contained in the aqueous coating composition of the present invention satisfy specific conditions, the present invention can more effectively achieve both peel strength and adhesion between the release layer and the substrate film.

[0032] The present invention will be described in detail below.

[0033] <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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] In one embodiment, the surface layer A does not contain particles having a particle size of less than 1.0 μm, so that defects caused by the transfer of particle shapes in the substrate to the resin sheet can be more effectively prevented.

[0042] 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 thereof, which more effectively prevents defects caused by the transfer of particle shapes in the substrate to the resin sheet.

[0043] For example, it is preferable that the surface layer A substantially does not contain particles having a particle size of less than 1.0 μm, and also substantially does not contain particles having a particle size of 1.0 μm or more.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] <Release Layer> In the present invention, the release layer is laminated on the substrate film, for example, the release layer is laminated on the surface layer A of the substrate. The release layer of the present invention is a layer formed by reacting and solidifying an aqueous coating composition.

[0057] The aqueous coating composition comprises an alkenyl group-containing silicone (A), an Si—H group-containing silicone (B), and a silane coupling agent (C), and the content of (C) is 15 parts by mass or more when the total amount of (A), (B), and (C) is 100 parts by mass. With this configuration, the present invention can more effectively achieve both peel strength and adhesion between the release layer and the substrate film, and can exhibit good releasability even for green sheets having a thickness of 1.0 μm or less.

[0058] (Alkenyl Group-Containing Silicone (A)) The number average molecular weight of the alkenyl group-containing silicone (A) is preferably 1,000 or more and 50,000 or less. For example, it may be 1,000 or more and less than 50,000. It is more preferably 1,000 or more and 30,000 or less, and even more preferably 1,000 or more and 15,000 or less.

[0059] When the number average molecular weight is 1,000 or more and 50,000 or less, the emulsification properties into an aqueous coating composition tend to be good, and the coating uniformity also tends to be good.

[0060] Examples of alkenyl group-containing silicones include organopolysiloxanes represented by the following general formula (I).

[0061]

[0062] (In general formula (I), R1 may be the same or different and is an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms, including an alkyl group or a phenyl group; [SiO] b1 Y1s bonded to silicon atoms represented by the formula (II) may be the same or different, and are each an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms, including an alkyl group or a phenyl group, or are represented by general formula (II), in which R1 may be the same group as at least one R1 in general formula (I), and in which R1s in general formula (II) may be the same or different.

[0063]

[0064] [SiO] of general formula (I) a1 [SiO] c1 , [SiO] of general formula (II) d1 R1 bonded to the silicon atom represented by the formula (I) is preferably an alkenyl group having 2 to 8 carbon atoms, or a monovalent hydrocarbon group containing an alkyl group or a phenyl group. For example, [SiO] a1 [SiO] c1 [SiO] d1 At least one of R1's bonded to the silicon atom represented by the formula (I) is an alkenyl group having 2 to 8 carbon atoms.

[0065] In one embodiment, the terminal R1 can also be an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group containing an alkyl group or a phenyl group. For example, the terminal R1 is preferably an alkenyl group having from 2 to 8 carbon atoms or a methyl group. A terminal alkenyl group is particularly preferred because it causes relatively little steric structural hindrance when reacted with a Si—H group, making it easy to improve releasability.

[0066] Examples of the alkenyl group having 2 to 8 carbon atoms represented by R1 include a vinyl group, a phenyl group, a butenyl group, a pentenyl group, and a hexenyl group, and among these, a vinyl group is particularly preferred.

[0067] [SiO] in general formula (I) and general formula (II) a1 [SiO] b1 [SiO] c1 [SiO] d1 When the total of the structural units is 100 mol%, [SiO] b1 The range of the structural unit is preferably 1 mol % or more and 99 mol % or less, and more preferably 2 mol % or more and 80 mol % or less. For example, [SiO] b1 The range of the structural unit may be 2 mol % or more and 50 mol % or less, or may be 2 mol % or more and 40 mol % or less.

[0068] Also, [SiO] b1 It is desirable that the number of structural units of the formula (I) is within the above range, and that the number average molecular weight of the alkenyl group-containing silicone (A) is within the range described in this specification.

[0069] Within the above range, the proportion of branched structures is adequate, the hydrocarbon groups are localized on the coating surface, and a dense film is formed, resulting in good peelability and coating uniformity of the release layer.

[0070] In the alkenyl group-containing silicone (A), the alkenyl group may be introduced at one end, both ends, or a side chain. The number of alkenyl groups in a molecule is two or more, preferably 2 to 20, more preferably 2 to 10. If there are two or more alkenyl groups, a crosslinked structure can be formed, and a sufficient number of crosslinking reaction points can be obtained. If there are 20 or less, the variation in the crosslinked structure can be reduced, and uniform releasability can be achieved. For example, the alkenyl group is introduced at one end or both ends. Furthermore, since the number of crosslinking reaction points is adequate, the size of foreign matter consisting of unmelted release layer contained in recycled resin produced from the release film can be reduced, which tends to improve recyclability.

[0071] In the aqueous coating composition, when the total amount of the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C) is taken as 100 parts by mass, the alkenyl group-containing silicone (A) is preferably contained in an amount of 15 parts by mass or more and less than 85 parts by mass, for example, 45 parts by mass or more and 83 parts by mass or less, or alternatively 50 parts by mass or more and 83 parts by mass or less, or even 51 parts by mass or more and 80 parts by mass or less.

[0072] When the content of the alkenyl group-containing silicone (A) is 15 parts by mass or more, the number of crosslinking reaction sites becomes sufficient, a dense crosslinked structure is easily formed, and releasability is improved, which is preferable. In particular, when the content of the alkenyl group-containing silicone (A) is 51 parts by mass or more, releasability from resin sheets such as ceramic green sheets, adhesion to substrates, and recyclability can be improved.

[0073] In addition, when the content of the alkenyl group-containing silicone (A) is less than 85 parts by mass, the alkenyl group in the release layer is less likely to remain, the activity of the release layer surface is less likely to increase, and the release property is maintained well, which is preferable. In addition, since the present invention contains the alkenyl group-containing silicone (A) in the above range and a predetermined amount of the silane coupling agent (C), it is thought that the effect of the release component of the entire release layer being rich, the release property being good, and the adhesion between the release layer and the substrate being compatible can be achieved.

[0074] For example, the release layer may contain a plurality of alkenyl group-containing silicones (A) each having a predetermined molecular weight.

[0075] The alkenyl group-containing silicone (A) preferably has a branched structure, because the presence of a branched structure gives the release layer a dense structure and improves releasability.

[0076] (Si—H Group-Containing Silicone (B)) The Si—H group-containing silicone (B) preferably has two or more Si—H groups (i.e., two or more hydrogen atoms directly bonded to Si atoms) in the molecule. The terminal silicon atom preferably has a trialkylsilane structure such as trimethylsilane.

[0077] The Si—H group-containing silicone (B) is exemplified by organohydrogenpolysiloxanes represented by the following general formula (III):

[0078]

[0079] (In general formula (III), a2 is preferably a natural number selected from 1 to 50, and b2 is preferably a natural number selected from 10 to 80. R2 may be the same or different and is a monovalent hydrocarbon group having from 1 to 16 carbon atoms, including an alkyl group or an aryl group.)

[0080] In the Si—H group-containing silicone (B) represented by the general formula (III), [SiO] a2 and [SiO] b2 When the total of the structural units is 100 mol%, [SiO] a2 The range of the structural unit is preferably 40 mol % or more and 80 mol % or less, and more preferably 45 mol % or more and 70 mol % or less. [SiO] a2 When the content of the structural unit [SiO] is 40 mol % or more, the number of crosslinking reaction sites becomes sufficient, the cohesive force of the release layer increases, and the abrasion resistance and solvent resistance of the release layer also become good, which is preferable. b2 The range of the structural unit is preferably 20 mol % or more and 60 mol % or less, and more preferably 30 mol % or more and 55 mol % or less. [SiO] b2 When the content of the structural unit of is 20 mol % or more, the amount of methyl groups localized on the surface of the release layer increases, which is preferable because the release layer has good releasability.

[0081] The number average molecular weight of the Si—H group-containing silicone (B) in the present invention is preferably 1,000 or more and 50,000 or less. For example, it may be 1,000 or more and less than 50,000. It is more preferably 1,000 or more and 30,000 or less, and even more preferably 1,000 or more and 15,000 or less.

[0082] When the number average molecular weight is 1,000 or more, sufficient releasability is easily obtained, while when the number average molecular weight is 50,000 or less, the emulsification properties into an aqueous coating composition are good, and coating uniformity also tends to be good.

[0083] In the aqueous coating composition, the Si—H group-containing silicone (B) is preferably contained in an amount of 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 19 parts by mass or less, and even more preferably 3 parts by mass or more and 18 parts by mass or less, relative to a total of 100 parts by mass of the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C). When the content of the Si—H group-containing silicone (B) is 1 part by mass or more, a sufficient number of crosslinking reaction sites are obtained, which facilitates the formation of a dense crosslinked structure and improves releasability, which is preferable. When the content of the Si—H group-containing silicone (B) is 20 parts by mass or less, Si—H groups are less likely to remain in the release layer and the amount of uncrosslinked material is reduced, which is preferable because good releasability is maintained.

[0084] (Silane Coupling Agent (C)) In the present invention, the silane coupling agent (C) has a structure having a hydrolyzable group bonded to a silicon atom and various organic functional groups, and is preferably a water-soluble or water-dispersible organic silane coupling agent.

[0085] Examples of the silane coupling agent (C) include compounds represented by the general formula (IV): YSiX3. 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 Y contains at least one functional group selected from these. It is particularly preferable that Y contains an epoxy group, a vinyl group, an acid anhydride, or a carboxyl group. Furthermore, Y and Si may be bonded via a methylene group or an ether group.

[0086] 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.

[0087] Examples of the silane coupling agent (C) include vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, p-styryltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, and triacetoxyvinylsilane.

[0088] Two or more types of silane coupling agents (C) may be used.

[0089] When two or more types of silane coupling agents are used in combination, a combination of a silane coupling agent having an epoxy group in Y in general formula (IV) and a silane coupling agent having a vinyl group in Y is preferred, and in particular, the silane coupling agent having an epoxy group is preferably a compound in which Y and Si are bonded via a methylene group or an ether group. The combined use of a silane coupling agent having an epoxy group in Y and a silane coupling agent having a vinyl group in Y is preferred because it provides good adhesion between the release layer and the substrate while also providing good releasability.

[0090] In another embodiment, a silane coupling agent having an epoxy group in Y and a silane coupling agent having a carboxyl group in Y may be used in combination.

[0091] The total content of the silane coupling agent (C) is preferably 15 parts by mass or more and 90 parts by mass or less, more preferably 15 parts by mass or more and 70 parts by mass or less, and preferably 15 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the total of the alkenyl group-containing silicone (A), Si—H group-containing silicone (B), and silane coupling agent (C) contained in the release layer. When the amount of the silane coupling agent (C) is 15 parts by mass or more and 90 parts by mass or less, the film of the release layer becomes hard and the releasability becomes good. In addition, the adhesion between the release layer and the substrate film is good, and it can be applied to thinning resin sheets such as ceramic green sheets.

[0092] Furthermore, foreign matter in the film, such as the release layer, can be reduced, and a release film with good recyclability can be obtained.

[0093] When a plurality of silane coupling agents (C) are contained, the total content of the silane coupling agents (C) may be within the above range.

[0094] On the other hand, when the total content of the silane coupling agent (C) is less than 15 parts by mass, the peel strength of the release film having the composition according to the present invention tends to be 0.2 mN / mm or more and less than 0.3 mN / mm. Such a release film can exhibit peelability from, for example, a green sheet having a thickness of 2.0 μm or more.

[0095] On the other hand, it does not exhibit sufficient releasability for green sheets and resin sheets having a thickness of 1.0 μm or less. While not limited to a specific theory, it is presumed that when the total content of the silane coupling agent (C) is less than 15 parts by mass, the number of crosslinking points (crosslinked structures) formed by the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C) becomes slightly less than the required characteristics. As a result, even if the hardness of the release layer is sufficient for the conventional required characteristics, it is presumed that the hardness becomes slightly insufficient for peeling off green sheets and resin sheets having a thickness of 1.0 μm or less.

[0096] Furthermore, it is desirable to reduce the peel force when peeling off green sheets and resin sheets having a thickness of 1.0 μm or less. The present inventors have succeeded in reducing the peel force of the release layer and improving the adhesion of the release layer to the substrate by adding a silane coupling agent (C), particularly a silane coupling agent having a functional group described herein, in the amount described in the present invention to a release film having an alkenyl group-containing silicone (A) and an Si—H group-containing silicone (B) in the release layer. While not limited to a specific theory, it is speculated that the functional group of the silane coupling agent having a functional group described herein serves as a crosslinking point in the release layer, contributing to the hardness of the release layer and reducing the peel force, and also contributing to the improved adhesion of the release layer to the substrate.

[0097] (Platinum-Based Catalyst) The crosslinking reaction between the alkenyl group-containing silicone (A) and the Si—H group-containing silicone (B) is an addition reaction, and in one embodiment, it is preferable to use a platinum-based catalyst to accelerate the reaction.

[0098] Known platinum catalysts can be used, such as platinum chloride and chloroplatinic acid. Taking into consideration dispersibility in silicone, the platinum catalyst may be a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt's catalyst), which can be dispersed simultaneously with the silicone emulsification to ensure uniform dispersion.

[0099] The content of the platinum catalyst is preferably in the range of 10 ppm to 400 ppm by mass of platinum element relative to the combined mass of the alkenyl group-containing silicone (A) and the Si—H group-containing silicone (B). By setting the content in this range, the silicone can be sufficiently cured and the generation of silicone aggregates can be suppressed, resulting in a release film with excellent surface properties. When the mass ratio of platinum element is equal to or less than the upper limit, the addition reaction between the alkenyl group and the Si—H group becomes moderate, tending to suppress the generation of silicone aggregates. From this perspective, the content of the platinum catalyst is more preferably 300 ppm or less, and even more preferably 200 ppm or less. Furthermore, when the mass ratio of platinum element is equal to or greater than the lower limit, the addition reaction proceeds sufficiently, making it less likely that poor curing of the silicone will occur. From this perspective, the content of the platinum catalyst is more preferably 15 ppm or more, and even more preferably 20 ppm or more.

[0100] (Aqueous Solvent) In addition to the alkenyl group-containing silicone (A) and the Si—H group-containing silicone (B), the aqueous coating composition typically contains an aqueous solvent, with water being preferred as the aqueous solvent. In one embodiment, an aqueous dispersion of an alkenyl group-containing silicone and an aqueous dispersion of an Si—H group-containing silicone are used to prepare the aqueous coating composition. As the aqueous dispersion of each silicone, an aqueous emulsion is preferably used. The aqueous coating composition is preferably substantially free of organic solvents and uses water as the dispersion medium. By being substantially free of organic solvents, the stability of the silicone emulsion is improved, and it is possible to prevent changes in the composition of the aqueous coating composition due to emulsion breakdown, as well as aggregation and gelation of the resin in the silicone emulsion.

[0101] "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.

[0102] By using an emulsion type that contains a water-based solvent, i.e., silicone resin dispersed in water, it can be applied without causing any adverse effects on the human body or the environment.

[0103] (Wettability Improver) In order to promote wetting of the base film when providing a release layer, it is preferable to add a wettability improver to the aqueous coating composition. Adding a predetermined amount of wettability improver can reduce unevenness in the thickness of the release layer. An example of the wettability improver is a surfactant. Examples of such surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, etc., and it is also possible to use one or more of these. In order to prevent aggregation of the respective aqueous silicone emulsions and not affect the silicone curing reaction, it is preferable to use a nonionic surfactant as an emulsifier.

[0104] The nonionic surfactant preferably has an HLB value in the range of 6 to 18, and more preferably in the range of 10 to 15. 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, alkylene oxide adducts of higher fatty acid glycerides, alkylene oxides having a siloxane skeleton, and alkylene oxide adducts of the diol portion of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. The HLB value is a value calculated using Griffin's formula. Using a nonionic surfactant with an HLB value outside this range as an emulsifier for the silicone aqueous dispersion may worsen unevenness in the release layer.

[0105] As the nonionic surfactant, the following commercially available products can be used: Examples include DOWSIL 501W Additive (manufactured by Dow-Toray Industries, Inc.), DOWSIL 67 Additive (manufactured by Dow-Toray Industries, Inc.), DOWSIL FZ-2233 (manufactured by Dow-Toray Industries, Inc.), KF-6017 (manufactured by Shin-Etsu Chemical Co., Ltd.), KF-6028 (manufactured by Shin-Etsu Chemical Co., Ltd.), KF-6028P (manufactured by Shin-Etsu Chemical Co., Ltd.), Olfine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.), Olfine E1004 (manufactured by Nissin Chemical Industry Co., Ltd.), Olfine E1020 (manufactured by Nissin Chemical Industry Co., Ltd.), Olfine E1030W (manufactured by Nissin Chemical Industry Co., Ltd.), and Olfine PD-002W (manufactured by Nissin Chemical Industry Co., Ltd.).

[0106] The wettability improver is preferably used in an amount of 0.1 to 40 parts by mass, more preferably 0.2 to 35 parts by mass, and even more preferably 0.5 to 30 parts by mass, based on 100 parts by mass of the total solid content. When the amount is 0.1 to 40 parts by mass, the surface tension can be reduced and uniform coating properties can be improved.

[0107] The wettability improver is preferably used in an amount of 3 parts by mass to 300 parts by mass, more preferably 4 parts by mass to 200 parts by mass, and even more preferably 5 parts by mass to 100 parts by mass, based on 100 parts by mass of the silane coupling agent. When the amount is 3 parts by mass to 300 parts by mass, the wettability is good, the thickness unevenness of the release layer can be reduced, and the adhesion is also good.

[0108] (Crosslinking Reaction Inhibitor) In one embodiment, a reaction inhibitor is preferably contained in the aqueous coating liquid to suppress the activity of the platinum-based catalyst at room temperature. Such a reaction inhibitor is preferably a reaction inhibitor having an alkynyl group. The reaction inhibitor having an alkynyl group is not particularly limited as long as it has an alkynyl group, but specific examples include 1-ethynyl-1-cyclohexanol, 4-ethyl-1-octyn-3-ol, 3-methyl-1-dodecyn-3-ol, 3,7,11-trimethyl-1-dodecyn-3-ol, 1,1-diphenyl-2-propyn-3-ol, 3-ethyl-6-ethyl-1-nonyn-3-ol, 3-methyl-1-pentadecyn-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 3-phenyl-1-butyn-3-ol. Since the present invention is an aqueous coating liquid, it is preferable to use the reaction inhibitors exemplified above that have an alkynyl group and a hydroxyl group, in view of the balance between affinity and solubility in water and coordination ability to platinum, as well as the boiling point. Alternatively, the platinum catalyst may be mixed with a general organopolysiloxane and used as an aqueous emulsion in order to be added to the aqueous coating liquid.

[0109] The content of the crosslinking reaction inhibitor is preferably 5 ppm or more and 1000 ppm or less, more preferably 10 ppm or more and 700 ppm or less, and even more preferably 20 ppm or more and 500 ppm or less, based on the mass of the aqueous coating composition used to form the release layer. When the content of the crosslinking reaction inhibitor is equal to or greater than the lower limit, the pot life is extended, the addition curing reaction of silicone is less likely to proceed at room temperature, and silicone aggregates tend to be less likely to occur. When the content of the crosslinking reaction inhibitor is equal to or less than the upper limit, the silicone is less likely to migrate to the counterpart material after peeling it off, and the amount of reaction inhibitor volatilized during heat treatment is reduced, so contamination inside the oven is less likely to occur.

[0110] (Other Components) In one embodiment, other additives such as antistatic agents, ultraviolet absorbers, pigments, colorants, organic or inorganic particles, lubricants, antiblocking agents, etc. may be mixed into the aqueous coating composition within a range that does not impair the effects of the invention.

[0111] In the present invention, the thickness of the ceramic green sheet having good releasability is 1 μm or less.

[0112] <Preparation of Silicone Water Dispersion> An example of a method for preparing an aqueous emulsion is a method of emulsifying a predetermined alkenyl group-containing silicone or Si—H group-containing silicone, an aqueous solvent, and a surfactant. These components can be emulsified using a known method, such as a method of mechanically emulsifying a predetermined silicone and surfactant, and, if necessary, other components, prepared in advance, in an aqueous medium using a stirring device such as a homogenizer, an azihommixer, or an ultraplanetary mixer.

[0113] The particle size of the aqueous dispersion can be adjusted by adjusting the size of the stirring blade, the stirring speed, and the stirring time. The average particle size of the dispersed particles in each silicone aqueous dispersion is preferably 900 nm or less, and more preferably 100 nm or more and 800 nm or less.

[0114] <Formation of Release Layer> The release layer is formed by applying an aqueous coating composition containing an aqueous emulsion of an alkenyl group-containing silicone (A) and an aqueous emulsion of an Si—H group-containing silicone (B). In this case, a release layer is formed on at least one surface of the substrate film. The release layer is formed by applying the aqueous coating liquid to the substrate film, followed by heating and drying, whereby the components of the aqueous coating liquid react and solidify to form a release layer. The release layer is preferably formed during the film production process.

[0115] The thickness of the release layer is preferably 5 nm or more and 100 nm or less as the thickness after drying. If the thickness of the release layer is above the lower limit, sufficient releasability is easily obtained, and if it is below the upper limit, the peel strength tends not to increase, and there is no need to increase the concentration of the release layer component in the aqueous coating liquid or to increase the coating amount, which tends to make coating easier. Therefore, the thickness of the release layer is more preferably 5 nm or more and 70 nm or less, and even more preferably 5 nm or more and 50 nm or less. If the thickness of the release layer after drying is 5 nm or more and 100 nm or less, recyclability is good.

[0116] When the aqueous coating liquid is applied to a substrate film, the solid content is preferably 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less, based on the release layer components in the aqueous coating liquid. When the solid content of the release layer components in the aqueous coating liquid is above the lower limit, the film-forming properties tend to be good. When the solid content is below the upper limit, the stability of the aqueous coating liquid and the appearance of the release layer tend to be good. Water is preferably used as the aqueous solvent for adjusting the solid content.

[0117] The aqueous coating solution to be applied to the base film to form the release layer can be applied at any stage, but is preferably applied during the polyester film production 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.

[0118] 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, 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 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).

[0119] Among these, so-called in-line coating is preferred, in which an aqueous coating liquid 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. This allows coating and film formation to be carried out in a single process, which also leads to cost reduction. The release layer may be dried by a stretching process or heat setting treatment after coating, and a further drying process may be added as needed. Furthermore, when the composition is cured using a catalyst to obtain a cured coating, the composition can be cured by a stretching process or heat setting treatment, but a further curing process may be added as needed.

[0120] When applying an aqueous coating liquid to a polyester film, it is preferable to subject the film surface to a physical treatment such as corona surface treatment, flame treatment, or plasma treatment as a preliminary treatment to improve coatability, or to use the above-mentioned emulsifier together with the composition as a wetting agent, or to add a surfactant as a wetting agent.

[0121] Any known coating method can be used as the coating method, such as roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, curtain coating, etc., which can be used alone or in combination.

[0122] <Characteristics of Release Film> In the present invention, the surface free energy of the release layer is 10 mJ / m 2 40mJ / m or more 2 The following range is preferred, and more preferably 11 mJ / m 2 35mJ / m or more 2More preferably, 12 mJ / m or less 2 30mJ / m or more 2 Below 13 mJ / m, particularly preferably 2 25mJ / m or more 2 The surface free energy of the release layer is within the range below. If the surface free energy is below the upper limit, the adhesive force is reduced and heavy release is difficult to occur. On the other hand, if the surface free energy is above the lower limit, defects due to repelling of a processed layer such as a ceramic green sheet or a resin sheet coated on the surface of the release layer are difficult to occur, and pinhole defects are also difficult to occur.

[0123] <Uses> The release film of the present invention can be used as a process film used during the production of multilayer ceramic capacitors or during resin sheet casting. For example, it can also be called a release film for multilayer ceramic capacitors or a release film for resin sheets. The resin sheet may be a ceramic green sheet.

[0124] In particular, even when a thin film resin sheet having a thickness of 0.5 to 1 μm after drying is produced, the wettability is good, so pinholes in the processing layer are reduced, and when used as a release film for producing green sheets, for example, the defective rate of thin multilayer ceramic capacitors can be reduced.

[0125] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The physical properties and other properties in the following examples were evaluated using the following methods.

[0126] (1) Surface Free Energy of Release Layer For a sample 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 (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 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.

[0127]

[0128] 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

[0129] (2) Coating uniformity of release layer The release film was cut into an A4 size, and the release layer surface was visually observed using a fluorescent lamp and a halogen light. The number of aggregated coating defects (number per A4 size) was compared and evaluated according to the following criteria: ○: 5 or less coating defects △: 6 or more coating defects

[0130] (3) Ceramic Green Sheet Peelability 100 parts by weight of barium titanate (BaTiO3, manufactured by Kyoritsu Materials Co., Ltd.), 7 parts by weight of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd.), 3 parts by weight of dioctyl phthalate, and 3 parts by weight of a dispersant (DISPERBYK-103, manufactured by BYK-Chemie) were added to a 1:1 (volume ratio) toluene:ethanol mixed solvent and dispersed using a ball mill to prepare a slurry. This slurry was uniformly coated onto the release layer of a release film to a dry thickness of 1 μm or 2 μm, and then dried to form a ceramic sheet. The release film on which the ceramic green sheet was formed was cut into 30 mm x 80 mm specimens to prepare test pieces. The ceramic green sheet was then peeled off using a tensile tester at a peel angle of 90°, a peel temperature of 40°C, and a peel speed of 10 m / min, and the peel strength was measured. The peel strength of the ceramic green sheet was evaluated based on the following criteria. ◯: Peel strength is less than 0.2 mN / mm △: Peel strength is 0.2 mN / mm or more but less than 0.3 mN / mm ×: Peel strength is 0.3 mN / mm or more

[0131] (4) Rub-off test (adhesion) of release layer The release surface of the release film was rubbed with a thumb at a load of about 500 gf 10 times, and an adhesive tape (manufactured by Nitto Denko Corporation, product name "31B tape") was stuck to the rubbed surface to check for silicone detachment at that point. The peeling state of the adhesive tape was checked and evaluated according to the following criteria: ○: When the adhesive tape was peeled off, the peeling change was less than 1.5 times; ×: When the adhesive tape was peeled off, the peeling change was 1.5 times or more.

[0132] (5) Recyclability Evaluation Recyclability was evaluated by counting the number of particles with a maximum diameter of 50 μm or more, magnifying the size and number of particles contained in the film by 20 times using a universal projector. The measurement area was 0.05 m. 2 ◯: Number of foreign objects: 5 / 0.05m 2 Less than 5-10 foreign objects / 0.05m, no problem in use. 2 Less than 10 foreign objects / 0.05m, slightly affects flatness, but can be used for limited purposes. 2 It cannot be used any more.

[0133] (6) Number Average Molecular Weight: The number average molecular weight was measured by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.

[0134] (7) Thickness of the Release Layer After cutting the release film into small triangular pieces, a 2 nm thick Pt (platinum) layer was formed on the surface of the release layer by coating. The obtained sample was fixed in a multiaxial embedding capsule, embedded in epoxy resin, and sliced ​​perpendicular to the film surface using a microtome ULTRACUT-S to obtain an ultrathin sample with a thickness of 50 nm. The obtained ultrathin sample was then mounted on a grid and steam-stained with 2% osmic acid at 60 °C for 2 hours. Using the ultrathin sample after steam staining, the film cross section was observed using a transmission electron microscope LEM-2000 at an accelerating 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 (unit: nm).

[0135] (Alkenyl Group-Containing Silicone (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 90% by mass of silicone oil having a number average molecular weight of 45,000 and 10% by mass of polyoxyethylene tridecyl ether (manufactured by Lion Specialty Chemicals Co., Ltd., trade name "Leocol TD-90") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of sample (A-1) with a solids content of 50% by mass. The emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0136] (Alkenyl Group-Containing Silicone (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 93% by mass of silicone oil having a number average molecular weight of 10,000 and 7% by mass of polyoxyethylene tridecyl ether (manufactured by Lion Specialty Chemicals Co., Ltd., trade name "Leocol TD-90") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of sample (A-2) with a solids content of 50% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 185 nm by adjusting the stirring speed and stirring time during emulsification.

[0137] (Alkenyl Group-Containing Silicone (A-3)) 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 95% by mass of silicone oil having a number average molecular weight of 8,000 and 4% by mass of polyoxyethylene tridecyl ether (manufactured by Lion Specialty Chemicals Co., Ltd., trade name "Leocol TD-90") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of sample (A-3) with a solids content of 50% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 185 nm by adjusting the stirring speed and stirring time during emulsification.

[0138] (Alkenyl Group-Containing Silicone (A-4)) 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 96% by mass of silicone oil having a number average molecular weight of 5,000 and 6% by mass of polyoxyethylene tridecyl ether (manufactured by Lion Specialty Chemicals Co., Ltd., trade name "Leocol TD-90") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of sample (A-4) with a solids content of 50% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 185 nm by adjusting the stirring speed and stirring time during emulsification.

[0139] (Alkenyl Group-Containing Silicone (A-5)) 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 92% by mass of silicone oil having a number average molecular weight of 1,000 and 8% by mass of polyoxyethylene tridecyl ether (manufactured by Lion Specialty Chemicals Co., Ltd., trade name "Leocol TD-90") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of sample (A-5) with a solids content of 50% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0140] (Si—H group-containing silicone (B-1)) Using an emulsifier capable of stirring the entire container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), raw materials consisting of 90% by mass of silicone oil having a number average molecular weight of 45,000 and 10% 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 an aqueous emulsion of sample (B-1) with a solid content of 40% by mass. In addition, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0141] (Si—H group-containing silicone (B-2)) Using an emulsifier capable of stirring the entire container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), raw materials consisting of 90% by mass of silicone oil having a number average molecular weight of 10,000 and 6% 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 an aqueous emulsion of sample (B-2) with a solid content of 40% by mass. In addition, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[0142] (Si—H Group-Containing Silicone (B-3)) 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 92% by mass of silicone oil having a number average molecular weight of 4,000 and 10% 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 an aqueous emulsion of sample (B-3) with a solids content of 40% by mass. In addition, the emulsion particle size was adjusted to an average particle size of 182 nm by adjusting the stirring speed and stirring time during emulsification.

[0143] (Si—H Group-Containing Silicone (B-4)) 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 90% by mass of silicone oil having a number average molecular weight of 1,000 and 10% 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 an aqueous emulsion of sample (B-4) with a solids content of 40% by mass. In addition, the emulsion particle size was adjusted to an average particle size of 185 nm by adjusting the stirring speed and stirring time during emulsification.

[0144] The following silane coupling agents were used: (C-1) vinyltrimethoxysilane KBM-1003 (Shin-Etsu Chemical Co., Ltd.) (C-2) 3-glycidoxypropylmethyldimethoxysilane KBM-403 (Shin-Etsu Chemical Co., Ltd.) (C-3) tris-(trimethoxysilylpropyl)isocyanurate KBM-9659 (Shin-Etsu Chemical Co., Ltd.) (C-4) 3-mercaptopropylmethyldimethoxysilane KBM-802 (Shin-Etsu Chemical Co., Ltd.) (C-5) N-phenyl-3-aminopropyltrimethoxysilane KBM-573 (Shin-Etsu Chemical Co., Ltd.) (C-6) 3-methacryloxypropylmethyldimethoxysilane KBM-502 (Shin-Etsu Chemical Co., Ltd.) (C-7) p-styryltrimethoxysilane KBM-1403 (Shin-Etsu Chemical Co., Ltd.) (C-8) 3-acryloxypropyltrimethoxysilane KBM-5103 (manufactured by Shin-Etsu Chemical Co., Ltd.) (C-9) 3-isocyanatepropyltriethoxysilane KBE-9007N (manufactured by Shin-Etsu Chemical Co., Ltd.) (C-10) 3-trimethoxysilylpropylsuccinic anhydride X-12-967C (manufactured by Shin-Etsu Chemical Co., Ltd.) (C-11) triacetoxyvinylsilane GENIOSIL GF62 (manufactured by Wacker Asahi Kasei Co., Ltd.)

[0145] Aqueous Coating Composition Production Example 1 An aqueous coating composition was obtained by mixing alkenyl group-containing silicone (A-1), Si—H group-containing silicone (B-1), silane coupling agent (C-2), and water in the proportions shown in Table 2 so that the solids concentration was 4 mass %. At this time, 0.01 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 relative to the total weight of the aqueous coating composition.

[0146] <Aqueous Coating Composition Production Examples 2 to 21> 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.

[0147] Example 1 Polyethylene terephthalate ([η] = 0.64 dl / g, Tg = 78°C) containing 0.1% 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 film was then stretched 3.3 times in the machine direction at 80°C, and the aqueous coating liquid (aqueous coating composition) obtained in Production Example 1 was uniformly coated using a roll coater so that the product thickness would be the release layer thickness shown in Table 2. The aqueous coating liquid used was one that had been prepared within 24 hours.

[0148] 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 about 10 seconds to obtain a release film (thickness 25 µm) having a release layer formed by reacting and solidifying the aqueous coating liquid, and the evaluation was carried out. The evaluation results are shown in Table 2.

[0149] In addition, for each example and comparative example, parts of the release film that did not become products when the product rolls were collected, or parts of the release film that did not become products due to defects, etc., were crushed until the long diameter of the film pieces was approximately 5 mm or less, melted, and 40% by mass of the recycled raw material was used.

[0150] Examples 2 to 14 Release films were produced under the same conditions as in Example 1, except that aqueous coating compositions obtained in the same manner as in Production Examples 2 to 14 were used, and the above-mentioned evaluations were carried out. Detailed conditions and evaluation results are shown in Table 2A.

[0151] <Comparative Examples 1 to 7> In Comparative Examples 1 to 7, release films were produced under the same conditions as in Example 1, except that silicones with silane coupling agent (C) added in amounts outside the range of the present invention were used, and the aqueous coating solutions obtained in Production Examples 15 to 21 were used, and the above-mentioned evaluations were carried out. Detailed conditions and evaluation results are shown in Table 2B.

[0152]

[0153]

[0154] As shown in Table 2, in Examples 2, 4, 6, and 13, release films were obtained in which both the releasability and adhesion of the release layer were easily achieved, and the release layer had good uniform coating properties and recyclability. Furthermore, Examples 1, 3, 5, 7 to 12, and 14 exhibited minimal physical properties. In contrast, as shown in Table 3, in Comparative Examples 1 to 6, in which the amount of silane coupling agent added was small, releasability and adhesion tended to deteriorate, and in Comparative Example 7, recyclability tended to deteriorate even further.

[0155] The release film of the present invention can achieve both releasability from a ceramic green sheet in a release layer made of an aqueous coating composition and adhesion to a substrate, and further has the advantages of good recyclability and excellent wettability of the release layer surface to a ceramic slurry, making it extremely valuable in industrial applications.

Claims

1. A release film for forming a resin sheet, comprising a substrate film and a release layer formed by reacting and solidifying an aqueous coating composition, wherein the aqueous coating composition contains an alkenyl group-containing silicone (A), a Si—H group-containing silicone (B), and a silane coupling agent (C), and when the total amount of the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C) is taken as 100 parts by mass, the content of the silane coupling agent (C) is 15 parts by mass or more.

2. The release film for forming a resin sheet according to claim 1, wherein the alkenyl group-containing silicone (A) has a number average molecular weight of 1,000 or more and less than 50,000.

3. The release film for forming a resin sheet according to claim 1, wherein the alkenyl group-containing silicone (A) has a structure represented by general formula (I). (In general formula (I), R1 may be the same or different and is an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms, including an alkyl group or a phenyl group; [SiO] b1 Y1s bonded to silicon atoms represented by the formula (II) may be the same or different, and are each an alkenyl group having from 2 to 8 carbon atoms, or a monovalent hydrocarbon group having from 1 to 16 carbon atoms containing an alkyl group or a phenyl group, or are represented by the formula (II), in which R1 may be the same group as at least one R1 in the formula (I), and in which R1s in the formula (II) may be the same or different.

4. The release film for forming a resin sheet according to claim 1, wherein the content of the Si—H group-containing silicone (B) is 20 parts by mass or less when the total amount of the alkenyl group-containing silicone (A), the Si—H group-containing silicone (B), and the silane coupling agent (C) is taken as 100 parts by mass.

5. The release film for forming a resin sheet according to claim 1, wherein the number average molecular weight of the Si—H group-containing silicone (B) is 1,000 or more and less than 50,000.

6. The release film for forming a resin sheet according to claim 1, wherein the silane coupling agent (C) has at least one functional group selected from 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, and a carboxyl group.

7. The release film for forming a resin sheet according to claim 1, wherein the aqueous coating composition further contains a wettability improver.

8. The release film for forming a resin sheet according to claim 1, wherein the release layer 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.

9. The release film for forming a resin sheet according to claim 1, wherein the base film is a polyester film.

10. The release film for forming a resin sheet according to claim 1, wherein the resin sheet is a ceramic green sheet.

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