JP7614569B2 - Release film for ceramic green sheet manufacturing - Google Patents

Description

The present invention relates to a release film for producing ultra-thin ceramic green sheets, and more specifically, to a release film for producing ultra-thin ceramic green sheets that can suppress the occurrence of process defects due to pinholes and uneven thickness during the production of ultra-thin ceramic green sheets.

Conventionally, release films using a polyester film as a base material and laminating a release layer thereon have been used for molding ceramic green sheets for multilayer ceramic capacitors (hereinafter referred to as MLCCs), ceramic substrates, etc. In recent years, as multilayer ceramic capacitors become smaller and have larger capacities, the thickness of ceramic green sheets has also tended to become thinner. Ceramic green sheets are molded by applying a slurry containing ceramic components such as barium titanate and a binder resin to a release film and drying it. After printing electrodes on the molded ceramic green sheets and peeling them off from the release film, the ceramic green sheets are laminated, pressed, cut, fired, and coated with external electrodes to produce multilayer ceramic capacitors. Until now, when molding ceramic green sheets on the release layer surface of a polyester film, there was a problem that minute protrusions on the release layer surface affect the molded ceramic green sheets, making them prone to defects such as repelling and pinholes. For this reason, various methods have been developed to realize a release layer surface with excellent flatness (for example, Patent Document 1).

However, in recent years, ceramic green sheets have become thinner, and there is a demand for ceramic green sheets with a thickness of 1.0 μm or less, more specifically 0.2 μm to 1.0 μm. This has led to a demand for higher smoothness on the release layer surface. In addition, as the ceramic green sheet becomes thinner, its strength decreases. Therefore, it is preferable not only to smooth the release layer surface, but also to make the peeling force when peeling the ceramic green sheet from the release film low and uniform, and it is preferable to minimize the load on the ceramic green sheet when peeling it from the release film, so as not to damage the ceramic green sheet.

In recent years, there has been a demand to reduce the thickness of release films from the standpoint of reducing environmental impact and costs. However, reducing the thickness of release films reduces the smoothness of the release film surface, reduces the stiffness of the release film and makes it more susceptible to curling, which can lead to problems with poor running properties of the release film when molding ceramic green sheets and printing electrodes. More specifically, poor running properties of the release film can lead to poor uniformity during coating and molding of ceramic green sheets, resulting in non-uniform film thickness of ceramic green sheets and reduced printing accuracy in the electrode printing process, which can lead to problems with the defective rate of molded MLCCs.

As a method for suppressing the load on the ceramic green sheet during peeling, a method has been considered in which the release layer of the release film is made of an active energy ray curable component to increase the crosslink density of the release layer and improve the elastic modulus, thereby suppressing the elastic deformation of the release layer during peeling of the ceramic green sheet and reducing the peeling force (for example, Patent Documents 2 and 3).

However, simply increasing the crosslink density of the release layer, as in Patent Documents 2 and 3, can increase the cure shrinkage of the release layer, raising concerns that curling may occur in the release film after processing the release layer. In addition, as the thickness of the release film becomes thinner, curling becomes more pronounced, raising concerns that problems may occur when molding the ceramic green sheet.

JP 2000-117899 A International Publication No. 2013/145864 International Publication No. 2013/145865

The inventors of the present invention have conducted extensive research in light of the above-mentioned circumstances and have found that by using a specific material for the release layer of a release film, it is possible to achieve both a high crosslink density and low cure shrinkage in the release layer. The object of the present invention is to provide a release film for molding ceramic green sheets that does not curl even when the thickness of the release film is reduced, has good peelability and runnability, and is unlikely to cause pinhole defects in the extremely thin ceramic green sheets that are molded.

That is, the present invention comprises the following:
1. A release film for producing a ceramic green sheet, comprising a polyester film and a release layer laminated on at least one side thereof directly or via another layer, the release layer having a surface roughness (Sa) of 7 nm or less, and the release layer being formed by curing a coating film containing at least a urethane acrylate having 4 or more functional groups in one molecule and a release agent.
2. The release film for producing a ceramic green sheet according to the above item 1, wherein the release agent is polyorganosiloxane.
3. The release film for producing a ceramic green sheet according to the above item 1, wherein the release agent is an acrylic compound having a silicone component and an acrylate group in the side chain.
4. The release film for producing a ceramic green sheet according to any one of the above items 1 to 3, characterized in that the polyester film is a laminated film consisting of at least two layers, and the surface layer A of the laminated film on the side on which the release layer is laminated does not substantially contain particles.
5. The release film for producing a ceramic green sheet according to the above 4, characterized in that the surface layer B of the laminate film opposite to the surface layer A contains particles, the particles being silica particles and/or calcium carbonate particles, and the total particle content is 5000 to 15000 ppm relative to the total mass of the surface layer B.
6. A method for producing a ceramic green sheet, comprising molding a ceramic green sheet using the release film for producing a ceramic green sheet according to any one of the above items 1 to 5, wherein the molded ceramic green sheet has a thickness of 0.2 μm to 1.0 μm.
7. A method for producing a ceramic capacitor, comprising adopting the method for producing a ceramic green sheet as described in 6 above.

Compared to conventional release films for producing ceramic green sheets, the release film for producing ceramic green sheets of the present invention curls less, has good peelability and running properties, and exhibits less deformation of the release layer when the ceramic green sheet is peeled off. This makes it possible to provide a release film for producing ceramic green sheets that can reduce defects such as pinholes in ultra-thin ceramic green sheets with a thickness of 1 μm or less even when the release film is thin.

The present invention will be described in detail below.

The release film for producing ultra-thin ceramic green sheets of the present invention has a release layer on at least one side of a polyester film, and the release layer is formed by curing a coating film that contains at least a multifunctional urethane acrylate having four or more functional groups and a release agent. A preferred embodiment of the release film for producing ceramic green sheets is the release film for producing ceramic green sheets.

(Polyester film)
The polyester constituting the polyester film used as the substrate in the release film of the present invention is not particularly limited, and a film formed from a polyester generally used as a substrate for a release film can be used, but preferably, it is a crystalline linear saturated polyester consisting of an aromatic dibasic acid component and a diol component. For example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or a copolymer mainly composed of these resin components is more preferable, and a polyester film formed from polyethylene terephthalate is particularly preferable. The polyethylene terephthalate preferably has a repeating unit of ethylene terephthalate of 90 mol % or more, more preferably 95 mol % or more, and may be copolymerized with a small amount of other dicarboxylic acid components and diol components, but from the viewpoint of cost, it is preferable to use one produced only from terephthalic acid and ethylene glycol. In addition, known additives such as antioxidants, light stabilizers, ultraviolet absorbers, and crystallizing agents may be added within a range that does not inhibit the effects of the film of the present invention. The polyester film is preferably a polyester film because of its high bidirectional elastic modulus.

The intrinsic viscosity of the polyethylene terephthalate film is preferably 0.50 to 0.70 dl/g, and more preferably 0.52 to 0.62 dl/g. When the intrinsic viscosity is 0.50 dl/g or more, breakage is less likely to occur 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 the specified product width, and dimensional defects do not occur, which is preferable. In addition, it is preferable to thoroughly vacuum dry the raw material.

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

In the present invention, the stretching temperature during stretching of the polyester film is preferably equal to or higher than the second-order transition point (Tg) of the polyester. It is preferable to stretch the film 1 to 8 times, and particularly 2 to 6 times, in both the longitudinal and transverse directions.

The polyester film preferably has a thickness of 12 to 31 μm, more preferably 12 to 25 μm, and even more preferably 15 to 22 μm. If the film is 12 μm or thicker, there is no risk of deformation due to heat during film production, during the processing step of the release layer, or during molding of the ceramic green sheet, which is preferable. On the other hand, if the film is 31 μm or thinner, the amount of film to be discarded after use is not excessively large, which is preferable in terms of reducing the environmental load, and furthermore, it is preferable from an economical point of view, since less material per area of the release film is used.

The polyester film substrate may be a single layer or a multi-layer of two or more layers, but is preferably a laminated film having a surface layer A that does not substantially contain particles on at least one side. In the case of a laminated polyester film having a multi-layer structure of two or more layers, it is preferable to have a surface layer B that can contain particles on the opposite side of the surface layer A that does not substantially contain particles. As for the laminated structure, if the layer on the side to which the release layer is applied is the surface layer A, the layer on the opposite side is the surface layer B, and the other core layer is the core layer C, the layer structure in the thickness direction can be a laminate structure such as release layer/surface layer A/surface layer B, or release layer/surface layer A/core layer C/surface layer B. Of course, the core layer C may be a multi-layer structure. Also, the surface layer B may not contain particles. In that case, it is preferable to provide a coat layer containing particles and a binder on the surface layer B in order to impart slip properties for winding the film into a roll.

In the polyester film substrate of the present invention, the surface layer A forming the surface to which the release layer is applied is preferably substantially free of particles. In this case, the area average surface roughness (Sa) of the surface layer A is preferably 7 nm or less. If Sa is 7 nm or less, the film thickness of the release layer is 2.0 μm or less, and even if it is thinner, such as 0.5 μm or less, pinholes are less likely to occur during molding of the laminated ultra-thin ceramic green sheet, which is preferable. It can be said that the smaller the area average surface roughness (Sa) of the surface layer A, the more preferable it is, but it may be 0.1 nm or more. However, when an anchor coat layer or the like is provided on the surface layer A as described below, it is preferable that the coat layer does not substantially contain particles, and it is preferable that the area average surface roughness (Sa) after lamination of the coat layer is within the above range. In the present invention, "substantially free of particles" is defined by, for example, in the case of inorganic particles, being 50 ppm or less when the inorganic elements are quantified by fluorescent X-ray analysis, preferably 10 ppm or less, and most preferably a content below the detection limit. This is because even if particles are not actively added to the film, contaminants from foreign matter, or dirt adhering to the raw resin or the lines and equipment during the film manufacturing process, can come off and become mixed into the film.

In the case where the polyester film substrate in the present invention is a laminated film, the surface layer B, which forms the surface opposite to the surface layer A to which the release layer is applied, preferably contains particles from the viewpoint of the slipperiness of the film and the ease of air escape, and particularly preferably contains silica particles and/or calcium carbonate particles. The particle content contained is preferably 5000 to 15000 ppm in total of particles in the surface layer B. In this case, the area surface average roughness (Sa) of the film of the surface layer B is preferably in the range of 1 to 40 nm, and more preferably in the range of 5 to 35 nm. When the total amount of silica particles and/or calcium carbonate particles in the surface layer B is 5000 ppm or more and Sa is 1 nm or more, air can be uniformly released when the film is wound up into a roll, and the film has a good rolled appearance and good flatness, making it suitable for the production of ultra-thin ceramic green sheets. Furthermore, when the total amount of silica particles and/or calcium carbonate particles is 15,000 ppm or less and Sa is 40 nm or less, the lubricant is less likely to aggregate and coarse protrusions are not formed, so even when an ultra-thin ceramic green sheet is rolled up after molding, defects such as pinholes are not generated in the ceramic green sheet, which is preferable.

As the particles contained in the surface layer B, it is more preferable to use silica particles and/or calcium carbonate particles from the viewpoints of transparency and cost. In addition to silica and/or calcium carbonate, inactive inorganic particles and/or heat-resistant organic particles can be used, and other usable inorganic particles include alumina-silica composite oxide particles and hydroxyapatite particles. In addition, examples of heat-resistant organic particles include cross-linked polyacrylic particles, cross-linked polystyrene particles, and benzoguanamine particles. In addition, 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.

The average particle diameter of the particles added to the surface layer B is preferably 0.1 μm or more and 2.0 μm or less, and particularly preferably 0.5 μm or more and 1.0 μm or less. If the average particle diameter of the particles is 0.1 μm or more, the slipperiness of the release film is good, which is preferable. Also, if the average particle diameter is 2.0 μm or less, there is no risk of pinholes due to coarse particles occurring on the surface of the release layer, which is preferable. The average particle diameter of the particles can be measured by observing the particles on the cross section of the processed film with a scanning electron microscope, observing 100 particles, and taking the average value as the average particle diameter. As long as the object of the present invention is satisfied, the shape of the particles is not particularly limited, and spherical particles and irregular non-spherical particles can be used. The particle diameter of irregular particles can be calculated as the circle equivalent diameter. The circle equivalent diameter is the value obtained by dividing the area of the observed particles by pi (π), calculating the square root, and multiplying it by two.

Surface layer B may contain two or more types of particles made of different materials. It may also contain particles of the same type but with different average particle sizes.

When surface layer B does not contain particles, it is also preferable to provide surface layer B with a coating layer containing particles to provide slipperiness. There are no particular limitations on the means for providing this coating layer, but it is preferable to provide it by the so-called in-line coating method, in which the coating is applied during the production of the polyester film.

The average surface roughness (Sa) of the surface layer B is preferably 40 nm or less, more preferably 35 nm or less, and even more preferably 30 nm or less. In addition, when the surface layer B is provided with a coating layer to provide slipperiness, the Sa of the surface layer B is measured on the surface on which the coating layer is laminated.

In order to reduce pinholes, it is preferable not to use recycled materials for the surface layer A, which is the layer on which the release layer is provided, in order to prevent the inclusion of particles such as lubricants.

The thickness ratio of the surface layer A, which is the layer on which the release layer is provided, is preferably 20% or more and 50% or less of the total layer thickness of the base film. If it is 20% or more, the film is less susceptible to the effects of particles contained in the surface layer B, etc. from the inside, and it is easy for the area 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 impact.

From an economical standpoint, layers other than the surface layer A (surface layer B or the aforementioned core layer C) can be made from 50 to 90% by mass of recycled raw materials such as film scraps or PET bottles. Even in this case, it is preferable that the type and amount of lubricant contained in the surface layer B, the particle size, and the area surface average roughness (Sa) satisfy the above ranges.

In order to improve the adhesion of a release layer to be applied later, or to prevent static electricity, a coating layer may be provided on the surface of surface layer A and/or surface layer B before or after uniaxial stretching in the film-forming process, and corona treatment may also be performed. When a coating layer is also provided, the Sa of each layer is substituted with the measured value of the coating layer surface. When these coating layers are provided on the surface of surface layer A, it is preferable that they do not contain particles.

(Release Layer)
The release layer of the present invention is preferably formed by curing a coating film containing at least a urethane acrylate having a functional group of 4 or more and a release agent. By using a urethane acrylate having a functional group of 4 or more, the crosslinking density can be improved while suppressing the curing shrinkage of the release layer, so that the elastic modulus of the release layer can be improved and deformation during peeling can be reduced. In addition, it is preferable because the solvent resistance of the release layer can be improved, so that erosion of the release layer by a solvent during slurry coating can be prevented.

(Urethane acrylate)
The urethane acrylate used in the present invention refers to one having a urethane bond in the molecular chain and one or more reactive functional groups selected from an acryloyl group and a methacryloyl group. In the present invention, the term urethane acrylate is used as a term including urethane methacrylate. The urethane acrylate used in the present invention preferably has four or more reactive functional groups in one molecule, more preferably six or more, and even more preferably nine or more. Having four or more reactive functional groups improves the crosslink density of the release layer and increases the elastic modulus, which is preferable because the deformation of the release layer is reduced when the ceramic green sheet is peeled off. In addition, the upper limit of the reactive functional groups is not particularly specified, but is preferably 20 or less, more preferably 15 or less. In this specification, when a hexafunctional urethane acrylate is mentioned, it refers to a urethane acrylate having six reactive functional groups in one molecule.

The urethane acrylate used in the present invention may be a monomer or an oligomer, or may be a mixture of a monomer and an oligomer. The weight average molecular weight (Mw) of the urethane acrylate used in the present invention is not particularly limited, but is preferably 600 to 20,000, more preferably 800 to 10,000, and even more preferably 1,000 to 5,000.
The weight average molecular weight Mw is a polystyrene equivalent value measured by GPC (gel permeation chromatography).

The synthesis method of the urethane acrylate used in the present invention is not particularly limited, but it can be obtained, for example, by reacting a polyhydric alcohol and an organic polyisocyanate with a hydroxy acrylate.

Examples of the polyhydric alcohols include neopentyl glycol, 3-methyl-1,5-pentanediol, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, tricyclodecane dimethylol, bis-[hydroxymethyl]cyclohexane, etc.; polyester polyols obtained by reacting the polyhydric alcohols with polybasic acids (e.g., succinic acid, phthalic acid, hexahydrophthalic anhydride, terephthalic acid, adipic acid, azelaic acid, tetrahydrophthalic anhydride, etc.); polycaprolactone polyols obtained by reacting the polyhydric alcohols with ε-caprolactone; polycarbonate polyols (e.g., polycarbonate diols obtained by reacting 1,6-hexanediol with diphenyl carbonate, etc.); and polyether polyols. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene oxide-modified bisphenol A.

The above organic polyisocyanates include, for example, isocyanate compounds such as isophorone diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, xylene diisocyanate, diphenylmethane-4,4'-diisocyanate, and dicyclopentanyl isocyanate, as well as adducts of these isocyanate compounds and polymers of these isocyanates.

Examples of the hydroxy(meth)acrylate compound include pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol tetra(meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate, dimethylolcyclohexyl mono(meth)acrylate, and hydroxycaprolactone(meth)acrylate. Among these, pentaerythritol tri(meth)acrylate and dipentaerythritol penta(meth)acrylate are preferred in terms of hardness.

The urethane acrylate used in the present invention may be commercially available. Examples of commercially available products include UV1700B (weight average molecular weight 2000, 10 functional groups), UV7620EA (weight average molecular weight 4100, 9 functional groups), UV7600B (weight average molecular weight 1400, 6 functional groups), UV7610B (weight average molecular weight 11000, 9 functional groups), UV7650B (weight average molecular weight 2300, 5 functional groups), DPHA40H (weight average molecular weight 7000, 10 functional groups), UX5003 (weight average molecular weight 700, 6 functional groups), Beamset 577 (weight average molecular weight 1000, 6 functional groups), 8UX-015A (weight average molecular weight 1000, 15 functional groups), and U15HA (weight average molecular weight 2300, 15 functional groups), manufactured by Nippon Synthetic Chemical Industry Co., Ltd.

In the present invention, the urethane acrylate may be used alone or in combination of two or more types. In addition, in addition to the urethane acrylate having four or more functional groups, an acrylate compound or a urethane acrylate compound may be contained within a range that does not impair the effects of the present invention. The acrylate compound may be an acrylate monomer or an acrylate oligomer, and the number of functional groups is not particularly limited, but it is preferable that the compound has two or more functional groups. In addition, when two or more types are contained, it is preferable that the compound contains 30% by mass or more of the urethane acrylate having four or more functional groups in order to achieve the effects of the present invention.

(Photoradical initiator)
When a radical polymerization resin is used in the release layer of the present invention, it is preferable to add a photoradical polymerization initiator.Specific examples of the photoradical polymerization initiator include benzophenone, acetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoic acid, benzoin methyl benzoate, benzoin dimethyl ketal, 2,4-diethylthioxanthone, 1-hydroxycyclohexyl phenyl ketone, benzyl diphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, β-chloroanthraquinone, (2,4,6-trimethylbenzyldiphenyl)phosphine oxide, and 2-benzothiazole-N,N-diethyldithiocarbamate. In particular, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methylpropan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, which are considered to have excellent surface curing properties, are preferred, and among these, 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one are particularly preferred. These may be used alone or in combination of two or more.

The amount of photoradical polymerization initiator added is not particularly limited. For example, it is preferable to use about 0.1 to 20% by mass of the radical curable resin used.

(Release Agent)
As the release agent (additive for improving the releasability of the release layer) used in the release layer of the present invention, a silicone-based additive or a non-silicone-based additive such as an olefin-based, long-chain alkyl-based, or fluorine-based additive can be used, but it is preferable to use a silicone-based additive from the viewpoint of releasability.

Silicone-based additives are compounds that have a silicone skeleton in the molecule, and polyorganosiloxanes and the like can be preferably used. Acrylic resins and alkyd resins that have polyorganosiloxanes on their side chains can also be used. Among polyorganosiloxanes, polydimethylsiloxane (abbreviated as PDMS) can be preferably used, and polydimethylsiloxanes that have functional groups in part are also preferred.

The functional group to be introduced into the polydimethylsiloxane is not particularly limited, and may be either a reactive functional group or a non-reactive functional group. The functional group may be introduced into one end of the polydimethylsiloxane, or into both ends or into a side chain. The position at which the functional group is introduced may be one or more. Two or more types of functional groups may be present in one molecule.

Reactive functional groups that can be introduced into polydimethylsiloxane include amino groups, epoxy groups, hydroxy groups, mercapto groups, carboxyl groups, methacryl groups, and acrylic groups. Non-reactive functional groups that can be used include polyether groups, aralkyl groups, fluoroalkyl groups, long-chain alkyl groups, ester groups, amide groups, and phenyl groups. In the present invention, in order to reduce migration of the release agent to the ceramic green sheet, it is preferable to use a release agent having a methacryl group or acrylic group that reacts with urethane acrylate.

It is also preferable to use polydimethylsiloxane-modified resins such as acrylic resins, polyester resins, and urethane resins having polydimethylsiloxane in the side chain. Polydimethylsiloxane-modified resins are more compatible with urethane acrylate than other general release agents and can form a uniform release layer, so they are preferable because they improve the releasability. Furthermore, it is more preferable for the polydimethylsiloxane-modified resin to have a methacrylic group or an acrylic group that reacts with urethane acrylate in order to reduce the migration of the release agent to the ceramic green sheet.
Examples of commercially available acrylic resins having a PDMS skeleton in the side chain include SYMAC (registered trademark) US350, SYMAC (registered trademark) US352 (manufactured by Toa Gosei Co., Ltd.), 8BS-9000 (manufactured by Taisei Fine Chemical Co., Ltd.), GL-01, and GL-02R (manufactured by Kyoeisha Chemical Co., Ltd.).
Examples of commercially available acrylic resins having a PDMS skeleton and an acryloyl group on the side chain include 8SS-723 (manufactured by Taisei Fine Chemical Co., Ltd.), GL-03, and GL-04R (manufactured by Kyoeisha Chemical Co., Ltd.).

There are no particular limitations on the fluorine-based additives, and existing ones can be used. For example, those with perfluoro groups or perfluoroether groups can be suitably used. Commercially available products include Megafac (registered trademark) (manufactured by DIC Corporation) and Optool (registered trademark) (manufactured by Daikin Industries, Ltd.).

As the long-chain alkyl additive, a resin modified with a long-chain alkyl can be used, and preferably, polyvinyl alcohol, acrylic resin, or the like, has an alkyl group having about 8 to 20 carbon atoms in the side chain. Also, a copolymer having a (meth)acrylic acid ester as the main repeating unit and containing a long-chain alkyl group having 8 to 20 carbon atoms in the transesterified portion can be suitably used.
In addition, octyl acrylate, lauryl acrylate, stearyl acrylate, and the like in which an acrylate group is attached to a long-chain alkyl group can also be suitably used.

In the release layer of the present invention, the release agent is preferably contained in an amount of 0.1% by mass or more and 15% by mass or less based on the solid content of the entire release layer. More preferably, it is 0.5% by mass or more and 10% by mass or less, and even more preferably, it is 0.5% by mass or more and 5% by mass or less. If it is 0.1% by mass or more, the release property is improved and the peelability of the ceramic green sheet is improved, which is preferable. On the other hand, if it is 15% by mass or less, the elastic modulus of the entire release layer is not excessively decreased, and the release layer is less likely to deform when the ceramic green sheet is peeled off, which is preferable. In this case, the solid content of the entire release layer is the sum of the solid content of the urethane acrylate component and the solid content of the release agent.

The release layer of the present invention may contain particles having a particle diameter of 1 μm or less, but from the viewpoint of preventing pinhole formation, it is preferable that the layer does not contain particles that form protrusions.

Additives such as adhesion improvers and antistatic agents may be added to the release layer of the present invention as long as they do not impair the effects of the present invention. In addition, in order to improve adhesion to the substrate, it is also preferable to perform pretreatment such as anchor coating, corona treatment, plasma treatment, and atmospheric pressure plasma treatment on the polyester film surface before providing the release coating layer.

In the present invention, the thickness of the release layer may be set according to the purpose of use, and is not particularly limited, but is preferably in the range where the release layer after curing is 0.2 to 2.0 μm, more preferably 0.3 to 1.5 μm, even more preferably 0.4 to 1.2 μm, and even more preferably 0.6 to 1.0 μm. A release layer thickness of 0.2 μm or more is preferable because the curing property of the urethane acrylate is good and the elastic modulus of the release layer is improved, resulting in good peeling performance. In addition, a thickness of 2.0 μm or less is preferable because even if the release film becomes thin, curling is unlikely to occur and poor running properties do not occur during the process of molding and drying the ceramic green sheet.

The release film of the present invention preferably has a high smoothness of the release layer surface. Therefore, it is preferable that the area surface average roughness (Sa) of the release layer surface is 7 nm or less. It is even more preferable that the above-mentioned Sa is satisfied and the maximum protrusion height (P) of the release layer surface is 100 nm or less. Furthermore, it is preferable that the area surface average roughness (Sa) is 5 nm or less, and at the same time, it is particularly preferable that the maximum protrusion height (P) is 80 nm or less. If the area surface roughness (Sa) is 7 nm or less, defects such as pinholes do not occur during the formation of the ceramic green sheet, and the yield is good, which is preferable. If the above-mentioned Sa is satisfied and the maximum protrusion height (P) of the release layer surface is 100 nm or less, it is preferable that the risk of pinhole defects is further reduced. It can be said that the smaller the area surface average roughness (Sa), the more preferable it is, but it may be 0.1 nm or more, or it may be 0.3 nm or more. The smaller the maximum protrusion height (P), the better, but it can be 1 nm or more, or 3 nm or more.

The surface free energy of the release layer surface of the release layer film of the present invention is preferably 18 mJ/m ² or more and 40 mJ/m ² or less. More preferably, it is 21 mJ/m ² or more and 35 mJ/m ² or less, and even more preferably, it is 23 mJ/m ² or more and 30 mJ/m ² or less. If it is 18 mJ/m ² or more, it is preferable because it is difficult for cissing to occur when the ceramic slurry is applied and it can be applied uniformly. Also, if it is 40 mJ/m ² or less, it is preferable because there is no risk of the releasability of the ceramic green sheet being reduced. By setting it in the above range, it is possible to provide a release film that is free of cissing during application and has excellent releasability.

In the present invention, the method for forming the release layer is not particularly limited, and a method is used in which a coating liquid in which a release resin is dissolved or dispersed is spread by coating or the like on one side of the polyester film substrate, the solvent is removed by drying, and then the layer is cured.

When the release layer of the present invention is applied to the substrate film by solution coating, the drying temperature for drying the solvent is preferably 50° C. or more and 120° C. or less, more preferably 60° C. or more and 100° C. or less. The drying time is preferably 30 seconds or less, more preferably 20 seconds or less. Furthermore, after the solvent is dried, it is preferable to irradiate active energy rays to promote the curing reaction. As the active energy rays used at this time, ultraviolet rays, electron beams, X-rays, etc. can be used, but ultraviolet rays are easy to use and preferable. The amount of ultraviolet rays to be irradiated is preferably 30 to 300 mJ/cm ² in terms of light amount, more preferably 30 to 200 mJ/cm ^2. By setting it to 30 mJ/cm ² or more, the curing of the resin progresses sufficiently, and by setting it to 300 mJ/cm ² or less, the processing speed can be improved, so that the release film can be economically produced, which is preferable.

The atmosphere during irradiation with the active energy rays may be either ordinary air or a nitrogen gas atmosphere. In a nitrogen gas atmosphere, the oxygen concentration is reduced, which allows the radical reaction to proceed smoothly and improves the elastic modulus of the release layer. However, if irradiation in air does not cause any practical problems, irradiation in air is preferable from an economical point of view.

In the present invention, the surface tension of the coating liquid when applying the release layer is not particularly limited, but is preferably 30 mN/m or less. By setting the surface tension as described above, the wettability after application is improved and the unevenness of the coating surface after drying can be reduced.

As a method for applying the coating liquid, any known coating method can be used, for example, roll coating methods such as gravure coating and reverse coating, bar coating methods such as wire bars, die coating, spray coating, air knife coating, and other conventionally known methods can be used.

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. In the following, weight average molecular weight may be simply referred to as Mw. Polydimethylsiloxane may be simply referred to as PDMS.

(Base film thickness)
Using a Millitron (electronic microindicator), four 5 cm square samples were cut from four arbitrary points of the film to be measured, and measurements were taken at five points on each sample (total of 20 points), and the average value was taken as the thickness.

(Release layer thickness)
The thickness of the release layer was measured using an optical interference film thickness meter (F20, Filmetrics, Inc.) (calculated assuming that the refractive index of the release layer was 1.52).

(area surface roughness Sa, maximum protrusion height P)
The values were measured under the following conditions using a non-contact surface shape measurement system (VertScan R550H-M100, manufactured by Ryoka Systems Co., Ltd.). The average value of five measurements was used for the area surface average roughness (Sa), and the maximum protrusion height (P) was measured seven times, and the maximum of the five measurements excluding the maximum and minimum values was used.

(Measurement conditions)
Measurement mode: WAVE mode Objective lens: 10x 0.5x Tube lens Measurement area 936μm x 702μm
(Analysis conditions)
・Face correction: 4th order correction ・Interpolation process: Full interpolation

(Surface Free Energy)
Droplets of water (droplet volume 1.8 μL), diiodomethane (droplet volume 0.9 μL), and ethylene glycol (droplet volume 0.9 μL) were prepared on the release surface of the release film using a contact angle meter (Kyowa Interface Science Co., Ltd.: Fully automatic contact angle meter DM-701) under conditions of 25° C. and 50% RH, and the contact angles were measured. The contact angles were measured 10 seconds after each liquid was dropped onto the release film. The contact angle data of water, diiodomethane, and ethylene glycol obtained by the above method were calculated according to the Kitazaki-Hata theory to determine the dispersion component γsd, polar component γsp, and hydrogen bond component γsh of the surface free energy of the release film, and the sum of each component was taken as the surface free energy γs. This calculation was performed using the calculation software in this contact angle meter software (FAMAS).

(Evaluation of ceramic slurry coatability)
A composition consisting of the materials listed below was stirred and mixed, and dispersed for 30 minutes using a bead mill using glass beads having a diameter of 0.5 mm as a dispersion medium to obtain a ceramic slurry.
Toluene 76.3 parts by weight Ethanol 76.3 parts by weight Barium titanate (HPBT-1, manufactured by Fuji Titanium Co., Ltd.) 35.0 parts by weight Polyvinyl butyral 3.5 parts by weight (S-LEC (registered trademark) BM-S, manufactured by Sekisui Chemical Co., Ltd.)
DOP (dioctyl phthalate) 1.8 parts by mass Next, the release surface of the obtained release film sample was coated with an applicator so that the slurry would have a thickness of 1 μm after drying, and after drying at 90° C. for 1 minute, the coatability was evaluated according to the following criteria.
◯: No repelling or the like occurred and the entire surface was coated.
Δ: There is some repelling at the coating edge, but the coating is applied over almost the entire surface.
×: There was a lot of repelling and coating was not possible.

(Pinhole evaluation of ceramic green sheets)
The ceramic slurry was applied in the same manner as in the evaluation of the coatability of the ceramic slurry, except that the ceramic slurry was applied to the release surface of the release film so as to have a thickness of 0.8 μm to form a ceramic green sheet. After drying at 90° C. for 1 minute, the release film was peeled off to obtain a ceramic green sheet.
In the central region in the film width direction of the obtained ceramic green sheet, light was applied from the side opposite to the side coated with the ceramic slurry within an area of 25 ^cm2 , and the occurrence of pinholes through which light was transmitted was observed and visually evaluated according to the following criteria. The measurement was performed five times and the average value was used.
◎: No pinholes ○: Almost no pinholes (Guideline: 2 or less pinholes per measurement area)
△: Pinholes have occurred (Guideline: 5 or less pinholes per measurement area)
×: Many pinholes were found

(Evaluation of peelability of ceramic green sheets)
A composition consisting of the materials listed below was stirred and mixed, and dispersed for 60 minutes using a bead mill using glass beads having a diameter of 0.5 mm as a dispersion medium to obtain a ceramic slurry.
Toluene 38.3 parts by weight Ethanol 38.3 parts by weight Barium titanate (HPBT-1, manufactured by Fuji Titanium Co., Ltd.) 64.8 parts by weight Polyvinyl butyral 6.5 parts by weight (S-LEC (registered trademark) BM-S, manufactured by Sekisui Chemical Co., Ltd.)
DOP (dioctyl phthalate) 3.3 parts by mass Next, the release surface of the obtained release film sample was coated with an applicator so that the dried slurry would have a thickness of 10 μm, and dried at 90° C. for 1 minute to form a ceramic green sheet on the release film. The obtained release film with the ceramic green sheet was de-electrified using a static eliminator (Keyence Corporation, SJ-F020), and then peeled at a width of 30 mm, a peel angle of 90 degrees, and a peel speed of 10 m/min. The stress applied during peeling was measured and used as the peel force. The peelability was evaluated according to the following criteria.
⊚: Peeling was possible with a very light peeling force of 1.5 mN/ ^mm2 or less.
◯: Peeling was possible with a relatively light force of more than 1.5 mN/ ^mm2 and not more than 2.0 mN/ ^mm2 .
Δ: The peeling force was greater than 2.0 mN/ ^mm2 and could be peeled off with a light force of 7.0 mN/ ^mm2 or less.
×: A peeling force of more than 7.0 mN/ ^mm2 was required (including cases where peeling was not possible).

(Evaluation of curl of release film)
The release film sample was cut to a size of 10 cm x 10 cm, and heat-treated in a hot air oven at 90 ° C for 1 minute without applying tension to the release film. After that, it was taken out of the oven and cooled to room temperature, and then the release film sample was placed on a glass plate with the release surface facing up, and the height of the part floating from the glass plate was measured. At this time, the height of the part floating the most from the glass plate was taken as the measured value. Curl property was evaluated according to the following criteria.
⊚: Curl was 1 mm or less, and almost no curling was observed. ◯: Curl was more than 1 mm and 3 mm or less, and slight curling was observed.
Δ: Curl was greater than 3 mm and not greater than 10 mm, and curl was observed.
×: Curl was greater than 10 mm.

(Preparation of Polyethylene Terephthalate Pellets (PET (I)))
The esterification reaction apparatus used was a continuous esterification reaction apparatus consisting of a three-stage complete mixing tank having a stirrer, a partial condenser, a raw material inlet, and a product outlet. The amount of TPA (terephthalic acid) was 2 tons/hour, the amount of EG (ethylene glycol) was 2 moles per mole of TPA, and the amount of antimony trioxide was such that the Sb atom was 160 ppm in the produced PET. The slurry of these was continuously fed to the first esterification reactor of the esterification reaction apparatus and reacted at normal pressure for an average residence time of 4 hours at 255°C. Next, the reaction product in the first esterification reactor was continuously removed from the system and fed to a second esterification reactor, and EG distilled off from the first esterification reactor was fed into the second esterification reactor in an amount of 8 mass% based on the produced PET. Furthermore, an EG solution containing magnesium acetate tetrahydrate in an amount such that the produced PET had Mg atoms of 65 ppm, and an EG solution containing TMPA (trimethyl phosphate) in an amount such that the produced PET had P atoms of 40 ppm, were added, and the reaction was carried out at normal pressure for an average residence time of 1 hour at 260°C. Next, the reaction product from the second esterification reactor was continuously removed from the system and fed to a third esterification reactor, and reacted at normal pressure for an average residence time of 0.5 hours at ²⁶⁰ ° C. while adding, as a 10% EG slurry, 0.2 mass % of porous colloidal silica having an average particle size of 0.9 μm that had been subjected to dispersion treatment at an average treatment number of 5 passes at a pressure of 39 MPa (400 kg/cm 2 ) using a high-pressure disperser (manufactured by Nippon Seiki Co., Ltd.) and 0.4 mass % of synthetic calcium carbonate having an average particle size of 0.6 μm and having an ammonium salt of polyacrylic acid attached at 1 mass % per calcium carbonate. The esterification reaction product produced in the third esterification reactor was continuously fed to a three-stage continuous polycondensation reactor to carry out polycondensation, and then filtered through a filter made of sintered stainless steel fibers with a 95% cut diameter of 20 μm, followed by ultrafiltration and extrusion into water, followed by cooling and cutting into chips to obtain PET chips with an intrinsic viscosity of 0.60 dl/g (hereinafter referred to as PET(I)). The lubricant content in the PET chips was 0.6% by mass.

(Preparation of polyethylene terephthalate pellets (PET (II)))
On the other hand, in the above-mentioned production of PET chips, PET chips containing absolutely no particles such as calcium carbonate or silica and having an intrinsic viscosity of 0.62 dl/g were obtained (hereinafter, abbreviated as PET (II)).

(Preparation of polyethylene terephthalate pellets (PET (III)))
A PET chip was obtained in the same manner as PET (I) except that the type and content of the particles of PET (I) was changed to 0.75% by mass of synthetic calcium carbonate having an average particle size of 0.9 μm and having 1% by mass of ammonium salt of polyacrylic acid attached to calcium carbonate (hereinafter, abbreviated as PET (III)). The lubricant content in the PET chip was 0.75% by mass.

(Production of Laminated Film X1)
After drying, these PET chips were melted at 285°C, and melted at 290°C by a separate melt extruder, and filtered in two stages using a filter made of sintered stainless steel fibers with a 95% cut diameter of 15 μm and a filter made of sintered stainless steel particles with a 95% cut diameter of 15 μm. The mixture was joined in a feed block, and PET (I) was laminated as surface layer B (non-release surface layer) and PET (II) was laminated as surface layer A (release surface layer). The mixture was extruded (casted) at a speed of 45 m/min into a sheet, and electrostatically adhered and cooled on a casting drum at 30°C by an electrostatic adhesion method to obtain an unstretched polyethylene terephthalate sheet with an intrinsic viscosity of 0.59 dl/g. The layer ratio was adjusted to PET (I)/(II) = 60%/40% by calculating the discharge amount of each extruder. Next, this unstretched sheet was heated with an infrared heater, and then stretched 3.5 times in the longitudinal direction by the speed difference between the rolls at a roll temperature of 80°C. Thereafter, it was introduced into a tenter and stretched 4.2 times in the transverse direction at 140°C. Next, it was heat-treated at 210°C in a heat setting zone. Then, it was relaxed 2.3% in the transverse direction at 170°C to obtain a biaxially stretched polyethylene terephthalate film X1 having a thickness of 25 μm. The surface layer A of the obtained film X1 had an Sa of 2 nm, and the surface layer B had an Sa of 29 nm.

(Production of Laminated Film X2)
The layer structure and stretching conditions were the same as those of the laminated film X1, but the thickness was adjusted by changing the casting speed to obtain a biaxially stretched polyethylene terephthalate film X2 having a thickness of 22 μm. The surface layer A of the obtained film X2 had an Sa of 3 nm, and the surface layer B had an Sa of 29 nm.

(Production of Laminated Film X3)
The layer structure and stretching conditions were the same as those of the laminated film X1, but the thickness was adjusted by changing the casting speed to obtain a biaxially stretched polyethylene terephthalate film X3 having a thickness of 19 μm. The surface layer A of the obtained film X3 had a Sa of 4 nm, and the surface layer B had a Sa of 30 nm.

(Production of Laminated Film X4)
The layer structure and stretching conditions were the same as those of the laminated film X1, but the thickness was adjusted by changing the casting speed to obtain a biaxially stretched polyethylene terephthalate film X4 having a thickness of 12 μm. The surface layer A of the obtained film X4 had an Sa of 5 nm, and the surface layer B had an Sa of 35 nm.

(Laminated film X5)
As the laminate film X5, E5101 (Toyobo Ester (registered trademark) film, manufactured by Toyobo Co., Ltd.) having a thickness of 25 μm was used. E5101 is a film containing particles. The Sa of the surface layer A of the laminate film X5 was 24 nm, and the Sa of the surface layer B was 24 nm.

(Laminated film X6)
A 25 μm thick A4100 (Cosmoshine (registered trademark), manufactured by Toyobo Co., Ltd.) was used as the laminate film X6. A4100 does not substantially contain particles in the film, and a coating layer containing particles is provided by in-line coating on the surface layer B side. The Sa of the surface layer A of the laminate film X6 was 1 nm, and the Sa of the surface layer B was 2 nm.

Example 1
Coating solution 1 having the following composition was applied to the surface layer A of laminated film X1 using reverse gravure so that the release layer thickness after drying would be 0.8 μm, and after drying at 90° C. for 15 seconds, it was irradiated with ultraviolet light using a high-pressure mercury lamp so as to be 150 mJ/cm ^2, thereby obtaining a release film for producing an ultrathin ceramic green sheet. The obtained release film was coated with a ceramic slurry by the above-mentioned method, and the coatability, peelability, pinholes, curl, etc. were evaluated, and good evaluation results were obtained.
(Coating Solution 1)
Methyl ethyl ketone 39.5 parts by weight Isopropyl alcohol 38.5 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent: 1.0 part by mass (acryloyl group-containing PDMS modified acrylic resin, GL-04R, manufactured by Kyoeisha Chemical Co., Ltd., solid content 20% by mass)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Examples 2 to 6, Comparative Example 1)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the urethane acrylate was changed to a urethane acrylate having a different number of functional groups as shown in Table 1.

When the release films for producing ceramic green sheets prepared in Examples 1 to 6 and Comparative Example 1 above were evaluated, it was found that in Examples 1 to 6, which used a urethane acrylate with four or more functional groups, the release films showed little curl and good releasability, but when a urethane acrylate with three functional groups, as shown in Comparative Example 1, was used, the releasability was insufficient. From these results, it was found that in order to achieve both releasability and low curl, it is best to use a urethane acrylate with four or more functional groups, more preferably six or more.

(Examples 7 and 8)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the thickness of the release layer was set to the value shown in Table 1.

(Examples 9 and 10)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the thickness of the base film was changed to the thickness shown in Table 1.

(Examples 11 and 12)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the configuration of the base film was changed to a base film shown in Table 1.

Example 13
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the release agent was changed to Coating Solution 2 in which PDMS having an acryloyl group was used.
(Coating Solution 2)
Methyl ethyl ketone 39.5 parts by weight Isopropyl alcohol 39.3 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent: 0.2 parts by mass (acryloyl group-containing PDMS, BYK (registered trademark)-3500, manufactured by BYK-Chemie, solid content 100% by mass)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Example 14)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the release agent was changed to Coating Solution 3, which was a perfluoropolyether compound having an acryloyl group.
(Coating Solution 3)
Methyl ethyl ketone 39.5 parts by weight Isopropyl alcohol 39.0 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent: 0.5 parts by mass (acryloyl group-containing perfluoropolyether, Megafac (registered trademark) RS-75, manufactured by DIC Corporation, solid content 40% by mass)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Example 15)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the release agent was changed to Coating Solution 4 in which stearyl acrylate was used.
(Coating Solution 4)
Methyl ethyl ketone 39.5 parts by weight Isopropyl alcohol 39.3 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent: 0.2 parts by weight
(Stearyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd., solid content 100% by weight)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Example 16)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the release agent was changed to Coating Solution 5, which was a PDMS-modified acrylic resin having no acryloyl group.
(Coating Solution 5)
Methyl ethyl ketone 39.5 parts by weight Isopropyl alcohol 38.5 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent 1.0 part by weight
(PDMS modified acrylic resin, GL-02R, manufactured by Kyoeisha Chemical Co., Ltd., solid content 20% by mass)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Example 17)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the coating solution was changed to Coating Solution 6 in which the amount of release agent added was changed.
(Coating Solution 6)
Methyl ethyl ketone 37.5 parts by weight Isopropyl alcohol 36.5 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent: 5.0 parts by mass (acryloyl group-containing PDMS modified acrylic resin, GL-04R, manufactured by Kyoeisha Chemical Co., Ltd., solid content 20% by mass)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Example 18)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the coating solution was changed to Coating Solution 7 in which the amount of release agent added was changed.
(Coating Solution 7)
Methyl ethyl ketone 39.5 parts by weight Isopropyl alcohol 39.0 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Release agent: 0.5 parts by mass (acryloyl group-containing PDMS modified acrylic resin, GL-04R, manufactured by Kyoeisha Chemical Co., Ltd., solid content 20% by mass)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF) 1.0 part by mass

(Example 19)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the photoradical initiator was changed to Irgacure (registered trademark) 127 (manufactured by BASF Corporation).

(Comparative Example 2)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 13, except that the urethane acrylate was changed to a multifunctional acrylate (A-DPH, functional group number 6, Mw 578, manufactured by Shin-Nakamura Chemical Co., Ltd.) having no urethane moiety in the molecule.
Although the obtained release film enabled the ceramic green sheet to be peeled off, the release film curled significantly, raising concerns about problems in molding the ceramic green sheet.

(Comparative Example 3)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the base film was changed to a base film X5 (thickness 25 μm, E5101 (Toyobo Ester (registered trademark) film, manufactured by Toyobo Co., Ltd.) having a configuration containing particles therein, and the release layer thickness was changed to 0.3 μm.
The obtained release film had a thin release layer thickness compared to the surface irregularities of the base film, resulting in a high surface roughness Sa of the release layer surface, and defects such as pinholes occurring in the molded ceramic green sheet.

(Comparative Example 4)
A release film for producing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the coating solution was changed to Coating Solution 8 containing no release agent.
(Coating Solution 8)
Methyl ethyl ketone 40.0 parts by weight Isopropyl alcohol 39.0 parts by weight Urethane acrylate (functional group number 15, Mw 1000) 20.0 parts by weight (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by weight)
Photoradical initiator (Irgacure (registered trademark) 907, manufactured by BASF): 1.0 part by mass. Since the obtained release film contained no release agent, the molded ceramic green sheet could not be peeled off.

The release film for producing ceramic green sheets of the present invention has a superior release layer surface smoothness, and the surface of the release layer is less deformed and curled less after the ceramic green sheet is peeled off, so that even when ultra-thin ceramic green sheets with a thickness of 1 μm or less are molded, there are few defects such as pinholes, making it possible to produce good ceramic green sheets.

Claims (6)

A release film in which a release layer is laminated directly or via another layer on at least one surface of a polyester film, the surface roughness (Sa) of the release layer being 7 nm or less, and the release layer being formed by curing a coating film containing at least a urethane acrylate having 6 or more functional groups in one molecule and a release agent,
The release agent comprises a silicone-based release agent having an acryloyl group, stearyl acrylate or perfluoropolyether. The release film for producing ceramic green sheets according to claim 1, characterized in that the release agent is a polyorganosiloxane-based release agent having an acryloyl group. The maximum peak height (P) of the release layer is 100 nm or less;
The release film for producing a ceramic green sheet according to claim 1 . The polyester film is a laminated film consisting of at least two layers, and a surface layer A of the laminated film on the side on which the release layer is laminated is substantially free of particles,
The release film for producing a ceramic green sheet according to claim 1, characterized in that a surface layer B on the opposite side to the surface layer A of the laminate film contains particles, the particles being silica particles and/or calcium carbonate particles, and the total particle content is 5,000 to 15,000 ppm relative to the total mass of the surface layer B. A method for producing a ceramic green sheet, comprising molding a ceramic green sheet using the release film for producing ceramic green sheets according to claim 1, characterized in that the molded ceramic green sheet has a thickness of 0.2 μm to 1.0 μm. A method for manufacturing a ceramic capacitor, characterized by employing the method for manufacturing a ceramic green sheet according to claim 5.