JP7848815B2 - Release film for manufacturing ceramic green sheets - Google Patents

Description

This invention relates to a release film for manufacturing ceramic green sheets. More specifically, it relates to a release film for manufacturing ceramic green sheets that can prevent pinholes and localized thickness variations, and reduce static electricity during unwinding, even when the ceramic green sheet is made into a thin film.

Conventionally, a technique has been disclosed to resolve problems such as the front and back sides of a ceramic green sheet manufacturing release film sticking together (blocking) when stored in a rolled state, by making the surface roughness of the side opposite to the side with the release agent layer (back side) of the base film relatively rough (see, for example, Patent Document 1). However, this conventional technique had the problem of causing pinholes and localized thickness variations due to the large protrusions.

Therefore, a technique has been disclosed that attempts to prevent pinholes and localized thickness variations in the ceramic green sheet by filling the protrusions on the back surface with a coating layer to reduce the height of the protrusions (see, for example, Patent Document 2). However, with this conventional technique, although the protrusion height is reduced, the protrusion density is low, resulting in high pressure on the protrusions. When the ceramic green sheet is further thinned, this leads to the problem of pinhole formation.

Japanese Patent Publication No. 2003-203822 Japanese Patent Publication No. 2014-144636

This invention was made against the backdrop of the problems of the prior art. Specifically, the object of this invention is to provide an excellent release film for manufacturing ceramic green sheets that can prevent pinholes and localized thickness variations, and reduce static electricity during unwinding, even when the ceramic green sheet is thinned.

The inventors, through diligent research to achieve the above objective, have completed the present invention. Specifically, the present invention consists of the following configuration.

1. A release film for manufacturing ceramic green sheets, comprising a polyester film substantially free of inorganic particles as a base material, a release coating layer on one surface of the base material, and a smooth coating layer containing particles on the other surface, wherein the smooth coating layer is formed by curing a composition containing acrylic resin and a melamine-based crosslinking agent.

2. The release film for manufacturing ceramic green sheets according to the first description above, wherein the glass transition temperature of the acrylic resin is 50°C or higher and 110°C or lower.

3. The release film for manufacturing ceramic green sheets according to the first or second description above, wherein the hydroxyl value of the acrylic resin is 50 mg KOH/g or more and 450 mg KOH/g or less.

4. A release film for manufacturing ceramic green sheets according to any one of the first to third claims above, wherein the average surface roughness (Sa) of the slip-free coating layer is 1 nm to 25 nm, the maximum protrusion height (P) is 60 nm to 500 nm, and the average length (RSm) of the roughness curve elements is 10 μm or less.

5. A release film for manufacturing ceramic green sheets according to any one of the first to fourth descriptions above, wherein the thickness of the slip-free coating layer is 0.001 μm or more and 2 μm or less.

6. A method for manufacturing a ceramic green sheet using a release film for manufacturing ceramic green sheets as described in any of the above paragraphs 1 to 5.

7. The method for manufacturing a ceramic green sheet according to paragraph 6, wherein the thickness of the ceramic green sheet to be manufactured is 0.2 μm or more and 2.0 μm or less.

8. A method for manufacturing a ceramic capacitor using the ceramic green sheet manufacturing method described in paragraph 6 or 7 above.

According to the present invention, it is possible to provide an excellent release film for manufacturing ceramic green sheets that can prevent pinholes and localized thickness variations, and reduce static electricity during unwinding, even when the ceramic green sheet is made into a thin film.

The present invention will be described in detail below.

The release film for manufacturing ceramic green sheets of the present invention (hereinafter sometimes simply referred to as "release film") is a release film having a release coating layer on one side of a biaxially oriented polyester film, which is the base film, and a smooth coating layer containing particles on the other side.

To increase the density of protrusions on the smooth surface, a release film has been proposed that can accommodate the thinning of green sheets in recent years by keeping the average length (RSm) of the roughness curve elements of the smooth coating surface within a specific range (e.g., International Publication No. 2017/017354). This technology is preferable because, by increasing the protrusion density, it is possible to maintain a low protrusion height while achieving good winding properties and preventing pinholes and localized thickness variations.

In this invention, since the smooth coating layer is formed by curing a composition containing acrylic resin and a melamine-based crosslinking agent, the hardness of the smooth coating layer is appropriately increased, making deformation of the smooth coating layer less likely when wound up after coating. It is generally known that the larger the contact area between two objects, the greater the static charge generated when the two objects are separated. A small amount of deformation in the smooth coating layer reduces the contact area between the smooth coating layer and the release layer, which is preferable because it suppresses static charge generated when the release film roll is unwound. Low static charge is preferable because it prevents quality defects in ceramic capacitors caused by the adhesion of environmental foreign matter to the release surface. In recent trends towards thin-film ceramic sheets, even the adhesion of minute environmental foreign matter to the release surface, which was not a problem in the past, becomes problematic. Therefore, a release film having the composition of the smooth coating layer specified in this invention is effective, and it is even more preferable if the average length (RSm) of the roughness curve elements of the smooth coating layer is kept within a specific range.

(Base film)
In the present invention, the film preferably used as a base material is a film made of polyester resin, and is preferably a polyester film mainly containing at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Alternatively, it may be a film made of polyester in which a third component monomer is copolymerized as part of the dicarboxylic acid component or diol component of the polyester as described above. Among these polyester films, polyethylene terephthalate film is the most preferred in terms of the balance between physical properties and cost.

Furthermore, the aforementioned polyester film may be single-layered or multi-layered. Within the range that achieves the desired effects of the present invention, various additives may be incorporated into the polyester resin of each of these layers as needed. Examples of additives include antioxidants, lightfastness agents, gelation inhibitors, organic wetting agents, antistatic agents, and ultraviolet absorbers.

(Easy-slip coating layer)
The release film of the present invention has a slip-free coating layer on one surface of a polyester base film as described above. Preferably, the slip-free coating layer contains at least a binder resin and particles.

(Binder resin in the slip-free coating layer)
In the present invention, the binder resin constituting the smooth coating layer preferably contains an acrylic resin. The acrylic resin is preferably an acrylic resin having hydroxyl groups and carboxyl groups in its molecule. It is even more preferable that the constituent units having hydroxyl groups constitute 20 to 90 mol% of the total constituent units out of 100 mol%. It is preferable that the constituent units having hydroxyl groups constitute 20 mol% or more because it maintains the water solubility of the acrylic resin appropriately and forms a strong crosslinked structure with the melamine-based crosslinking agent. On the other hand, it is preferable that the amount is 90 mol% or less because the hydroxyl groups of the acrylic resin and the particles contained in the smooth coating layer do not cause extreme interaction and the particles are uniformly dispersed.

To introduce hydroxyl groups into acrylic resin, monomers having hydroxyl groups, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, or ring-opening adducts of γ-butyrolactone or ε-caprolactone to 2-hydroxyethyl (meth)acrylate, can be used as copolymerization components. Among these, 2-hydroxyethyl (meth)acrylate is preferred because it does not inhibit water solubility. Note that two or more of these may be used in combination. Needless to say, the acrylic resin referred to in this invention includes methacrylic resin.

The hydroxyl value of the acrylic resin is preferably 50 mg KOH/g or higher, more preferably 100 mg KOH/g or higher, and even more preferably 150 mg KOH/g or higher. A hydroxyl value of 50 mg KOH/g or higher is preferable because it results in good water solubility of the acrylic resin and the formation of a strong crosslinked structure with the melamine-based crosslinking agent.

The hydroxyl value of the acrylic resin is preferably 450 mg KOH/g or less, more preferably 400 mg KOH/g or less, and even more preferably 350 mg KOH/g or less. A hydroxyl value of 450 mg KOH/g or less is preferable because it prevents excessive interaction between the hydroxyl groups of the acrylic resin and the particles contained in the smooth coating layer, resulting in uniform particle dispersion.

The acrylic resin used in this invention is preferably a resin having carboxyl groups in addition to hydroxyl groups. The presence of carboxyl groups makes it easy to impart water solubility. Examples include monomers containing carboxyl groups such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid, and monomers containing acid anhydride groups such as maleic anhydride and itaconic anhydride.

The monomer containing a carboxyl group is preferably present in an amount of 4 mol% or more, and more preferably 10 mol% or more, of 100 mol% of the total constituent units of the acrylic resin. An amount of 4 mol% or more is preferable because it facilitates the imparting of water solubility. The monomer containing a carboxyl group is preferably present in an amount of 65 mol% or less, and more preferably 50 mol% or less. An amount of 65 mol% or less is preferable because the Tg of the resulting coating film does not become excessively high compared to the preferred range described later, resulting in good film-forming properties and stretchability in in-line coating.

To achieve good water solubility, it is preferable to neutralize the carboxyl groups introduced into the acrylic resin by copolymerization of acrylic acid or methacrylic acid. Suitable basic neutralizing agents include amine compounds such as ammonia, trimethylamine, triethylamine, and dimethylaminoethanol, as well as inorganic basic substances such as potassium hydroxide and sodium hydroxide. Of these, amine compounds are preferred as neutralizing agents due to their volatility and ease of cross-linking structure formation. Ammonia is the most preferred because it does not cause particle aggregation. The neutralization rate is preferably 30 mol% to 95 mol%, more preferably 40 mol% to 90 mol%. A neutralization rate of 30 mol% or higher is preferable because it ensures sufficient water solubility of the acrylic resin, facilitates dissolution of the acrylic resin during coating solution preparation, and prevents whitening of the coating surface after drying. On the other hand, a neutralization rate of 95 mol% or lower is preferable because it avoids excessive water solubility, facilitating mixing of alcohols and other substances during coating solution preparation.

The acid value of the acrylic resin is preferably 40 mg KOH/g or higher, more preferably 50 mg KOH/g or higher, and even more preferably 60 mg KOH/g or higher. An acid value of 40 mg KOH/g or higher is preferable because it facilitates the imparting of water solubility.

The acid value of the acrylic resin is preferably 400 mg KOH/g or less, more preferably 350 mg KOH/g or less, and even more preferably 300 mg KOH/g or less. A 400 mg KOH/g or less acid value is preferable because it prevents excessive interaction between the carboxyl groups of the acrylic resin and the particles contained in the smooth coating layer, resulting in uniform particle dispersion. Good particle dispersibility is preferable because it prevents the formation of large protrusions on the smooth coating surface and the occurrence of pinholes in the ceramic sheet.

The glass transition temperature (Tg) of the acrylic resin is preferably 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. A glass transition temperature of 50°C or higher is preferable because it results in a moderately high hardness of the smooth coating layer.

The glass transition temperature (Tg) of the acrylic resin is preferably 110°C or lower, more preferably 105°C or lower, and even more preferably 100°C or lower. A glass transition temperature of 110°C or lower is preferable because it allows for uniform stretching without cracking in the coating film during the stretching process after applying the smooth coating layer.

To achieve the above Tg range, (meth)acrylic monomers and non-acrylic vinyl monomers can be used as Tg-adjusting monomers copolymerized. Specific examples of (meth)acrylic monomers include alkyl (meth)acrylate esters such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and stearyl (meth)acrylate; nitrogen-containing acrylic monomers such as (meth)acrylamide, diacetone acrylamide, n-methylolacrylamide, and (meth)acrylonitrile; and vinyl methacrylate. One or more of these can be used.

Furthermore, examples of non-acrylic vinyl monomers include styrene monomers such as styrene, α-methylstyrene, vinyltoluene (a mixture of m-methylstyrene and p-methylstyrene), and chlorostyrene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl pivalate, vinyl octoate, vinyl monochloroacetate, divinyl adipate, vinyl crotate, vinyl sorbate, vinyl benzoate, and vinyl cinnamate; and halogenated vinyl monomers such as vinyl chloride and vinylidene chloride. One or more of these can be used.

For Tg adjustment, it is preferable to determine the appropriate amounts of hydroxyl group-containing monomers and carboxyl group-containing monomers, and then use the remainder. The Tg of the copolymer can be determined using the following Fox formula.

W _n : Mass fraction of each monomer (mass %)
Tg _n : Tg (K) of the homopolymer of each monomer

For Tg adjustment, it is preferable that the monomer copolymerized contains components that lower the surface free energy, such as long-chain alkyl groups. As an acrylic resin with introduced long-chain alkyl groups, it is preferable that the side chains of the acrylic resin have alkyl groups with approximately 8 to 20 carbon atoms. Furthermore, copolymers in which (meth)acrylic acid esters are the main repeating units and which contain long-chain alkyl groups with 8 to 20 carbon atoms in the transesterified portion can also be suitably used.

For Tg adjustment, the monomer having a long-chain alkyl group in the copolymerized monomer is preferably 50 mol% or less, and more preferably 40 mol% or less, of 100 mol% of the total constituent units of the acrylic resin. A concentration of 50 mol% or less is preferable because it prevents the Tg of the resulting coating film from becoming too low relative to the preferred range, thus maintaining a high level of coating film hardness. In this invention, the monomer having a long-chain alkyl group may be 0 mol% as long as the Tg can be maintained within the preferred range; however, a concentration of 5 mol% or more is preferable because it clearly demonstrates the effect of adjusting the Tg of the acrylic resin.

The acrylic resin used in this invention can be obtained by known radical polymerization. Emulsion polymerization, suspension polymerization, solution polymerization, bulk polymerization, etc., are all possible. Solution polymerization is preferred from the viewpoint of ease of handling. Examples of water-soluble organic solvents that can be used in solution polymerization include ethylene glycol n-butyl ether, isopropanol, ethanol, n-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, 1,3-oxolane, methyl solosolve, ethyl solosolve, ethyl carbitol, butyl carbitol, propylene glycol monopropyl ether, and propylene glycol monobutyl ether. These may also be used mixed with water.

Any known compound that generates radicals can be used as a polymerization initiator, but water-soluble azo polymerization initiators such as 2,2-azobis-2-methyl-N-2-hydroxyethylpropionamide are preferred. The polymerization temperature and time are selected as appropriate.

The mass-average molecular weight (Mw) of the acrylic resin is preferably around 10,000 to 200,000. A more preferable range is 20,000 to 150,000. An Mw of 10,000 or higher is preferable because there is no risk of thermal decomposition in the tenter. An Mw of 200,000 or lower is preferable because there is no significant increase in the viscosity of the coating solution, resulting in good coating properties.

In the present invention, other binder resins may be used in combination with acrylic resin as the binder for the smooth coating layer. Examples of other binder resins include polyester resin, urethane resin, polyvinyl resin (such as polyvinyl alcohol), polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, and starches.

The preferred content of the acrylic resin in the smooth coating layer is 20% to 95% by mass of the total solids. More preferably, it is 30% to 90% by mass. A content of 20% by mass or more is preferable because it prevents the amount of hydroxyl groups and carboxyl groups (the crosslinking components) from becoming too low, thus maintaining a high crosslink density. A content of 95% by mass or less is preferable because it prevents the amount of the crosslinking agent (the target of crosslinking) from becoming too low, thus maintaining a high crosslink density.

(Crosslinking agent)
In the present invention, it is preferable that the smooth coating layer contains a melamine-based crosslinking agent in order to form a crosslinked structure within the smooth coating layer. By including a melamine-based crosslinking agent, adhesion to the PET substrate can be improved, and the strength of the coating film of the smooth layer can be improved by promoting crosslinking with the hydroxyl groups and carboxyl groups of the acrylic resin, and as a result, static electricity when the release film roll is unwound can be suppressed. Other crosslinking agents may also be used in combination, and specific crosslinking agents that can be used in combination include urea-based, epoxy-based, oxazoline-based, carbodiimide-based, isocyanate-based, and silanol-based agents. Furthermore, catalysts and the like can be used as appropriate as needed to promote the crosslinking reaction.

As melamine-based crosslinking agents, for example, melamine, methylolated melamine derivatives obtained by condensing melamine with formaldehyde, compounds partially or completely etherified by reacting methylolated melamine with a lower alcohol, and mixtures thereof can be used. Specifically, compounds having triazine and a methylol group are particularly preferred. In the present invention, the melamine-based crosslinking agent refers to the component derived from the melamine-based crosslinking agent when the melamine-based crosslinking agent described below forms a crosslinked structure with the acrylic resin. The melamine-based crosslinking agent may be a monomer, a condensate consisting of dimers or more, or a mixture thereof. As lower alcohols used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol, etc. can be used. The groups include imino groups, methylol groups, or alkoxymethyl groups such as methoxymethyl or butoxymethyl groups, which are present in a single molecule. Examples include imino-type methylated melamine resins, methylol-type melamine resins, methylol-type methylated melamine resins, and fully alkyl-type methylated melamine resins. Among these, methylolated melamine resins are most preferred. Furthermore, to accelerate the thermosetting of the melamine compound, an acidic catalyst such as p-toluenesulfonic acid may be used.

Using such a melamine-based crosslinking agent not only suppresses static electricity during unwinding by increasing the hardness of the coating film due to the self-condensation of the melamine-based crosslinking agent, but also allows for the reaction between the hydroxyl groups and carboxyl groups contained in the acrylic resin and the melamine-based crosslinking agent to proceed, resulting in a resin layer with even higher hardness. This higher hardness coating film reduces deformation of the easily slippery coating layer during unwinding, resulting in a film with even greater suppression of static electricity during unwinding.

The preferred content of the crosslinking agent in the smooth coating layer is 5% by mass or more and 80% by mass or less of the total solid content. More preferably, it is 10% by mass or more and 70% by mass or less. A content of 5% by mass or more is preferable because it does not reduce the crosslinking density of the resin in the coating layer. A content of 80% by mass or less is preferable because it does not reduce the amount of hydroxyl groups and carboxyl groups in the acrylic resin to be crosslinked too much, thus preventing a decrease in crosslinking density.

(Particles in the slip-free coating layer)
The slip-free coating layer preferably contains lubricant particles to impart slipperiness to the surface. The particles may be inorganic or organic, and are not particularly limited, but examples include (1) inorganic particles such as silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, zirconium oxide, titanium dioxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, calcium carbonate, magnesium carbonate, calcium phosphate, magnesium hydroxide, and barium sulfate; and (2) organic particles such as acrylic or methacrylic, vinyl chloride, vinyl acetate, nylon, styrene/acrylic, styrene/butadiene, polystyrene/acrylic, polystyrene/isoprene, polystyrene/isoprene, methyl methacrylate/butyl methacrylate, melamine, polycarbonate, urea, epoxy, urethane, phenol, diallyl phthalate, and polyester. Silica is particularly preferred for providing the coating layer with appropriate lubricity.

The average particle size is preferably 10 nm or larger, more preferably 20 nm or larger, and even more preferably 30 nm or larger. An average particle size of 10 nm or larger is preferable because it reduces aggregation and ensures good lubricity.

The average particle size is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 600 nm or less. An average particle size of 1000 nm or less is preferable because it maintains transparency and prevents particle detachment.

Furthermore, for example, mixing small particles with an average particle size of approximately 10 to 270 nm with larger particles with an average particle size of approximately 300 to 1000 nm is preferable for achieving both slipperiness and smoothness while keeping the average surface roughness (Sa) and maximum protrusion height (P) low, as described later, and reducing the average length (RSm) of the roughness curve elements. Particularly preferable is the combination of small particles with an average particle size of 30 nm to 250 nm and larger particles with an average particle size of 350 to 600 nm. When mixing small and large particles, it is preferable to ensure that the mass content of the small particles is greater than the mass content of the large particles relative to the total solid content of the coated layer.

In terms of preventing particles from detaching from the smooth coating layer, the use of organic particles is particularly preferable. The use of organic particles strengthens the interaction between the binder and crosslinking agent components of the smooth coating layer, making it easier to prevent detachment, which is preferable. Among organic particles, acrylic resin particles and/or methacrylic resin particles, which have a chemical structure similar to the acrylic resin present in the smooth coating layer, are particularly preferable in terms of preventing particle detachment from the smooth coating layer. These organic particles are preferably included as particles with a relatively large average particle size, where particle detachment from the smooth coating layer is a common problem. For example, it is preferable to include particles with an average particle size of 300 to 1000 nm. Even more preferably, they are included as particles with an average particle size of 350 to 600 nm. Of course, it is particularly preferable that the organic particles with the above average particle size are acrylic resin particles and/or methacrylic resin particles.

The average particle size was measured by observing the particles in the cross-section of the processed film using a transmission electron microscope or scanning electron microscope. 100 non-aggregated particles were observed, and the average value of these 100 particles was used as the average particle size.

The particle shape is not particularly limited as long as it satisfies the objectives of this invention; spherical particles and irregularly shaped non-spherical particles can be used. The particle diameter of irregularly shaped particles can be calculated as the equivalent diameter. The equivalent diameter is obtained by dividing the observed particle area by π, calculating the square root, and multiplying by two.

The ratio of particles to the total solid content of the smooth coating layer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. A ratio of 50% by mass or less of particles to the total solid content of the smooth coating layer is preferable because it maintains transparency and prevents significant particle shedding from the smooth coating layer.

The ratio of particles to the total solid content of the slip-free coating layer is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. A ratio of 1% by mass or more of particles to the total solid content of the slip-free coating layer is preferable as it ensures sufficient slipperiness.

As a method for measuring the particle content in a slip-free coating layer, for example, if the slip-free coating layer contains both organic resin components and inorganic particles, the following method can be used. First, the slip-free coating layer applied to the processed film is extracted from the processed film using a solvent and allowed to dry. Next, heat is applied to the obtained slip-free coating layer, and the organic components contained in the slip-free coating layer are burned off by heat, thereby obtaining only the inorganic components. By measuring the weight of the obtained inorganic components and the slip-free coating layer before burning and distillation, the mass percentage of particles contained in the slip-free coating layer can be determined. At this time, accurate measurement can be achieved by using a commercially available differential thermal and thermogravimetric simultaneous measurement device. Note that the ratio of the above particles to the total solid content of the slip-free coating layer refers to the ratio of the total amounts of multiple types of particles if multiple types of particles are present.

(Additives in the lubrication coating layer)
In order to impart other functionalities to the smooth coating layer, various additives may be included, to the extent that they do not impair the appearance of the coating. Examples of such additives include fluorescent dyes, fluorescent whitening agents, plasticizers, ultraviolet absorbers, pigment dispersants, antifoaming agents, defoaming agents, and preservatives.

The smooth coating layer may contain surfactants to improve leveling during application and to defoam the coating solution. The surfactant can be cationic, anionic, or nonionic, but silicone-based, acetylene glycol-based, or fluorine-based surfactants are preferred. These surfactants should be included in the coating layer in an amount that does not cause abnormalities in the coating appearance due to excessive addition.

Regarding the coating method, both the so-called in-line coating method, where the coating is applied simultaneously during the formation of the polyester substrate film, and the so-called off-line coating method, where the coating is applied separately using a coater after the polyester substrate film has been formed, can be applied. However, the in-line coating method is more efficient and therefore preferable.

As a coating method, any known method can be used to apply the coating solution to polyethylene terephthalate (PET) film. Examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, and curtain coating method. These methods can be used individually or in combination.

In this invention, a method for providing a smooth coating layer on a polyester film includes applying a coating solution containing a solvent, particles, and resin to the polyester film and then drying it. As the solvent, examples include organic solvents such as toluene, water, or a mixture of water and a water-soluble organic solvent. However, from an environmental standpoint, a so-called aqueous solvent, such as water alone or a mixture of water and a water-soluble organic solvent, is preferred.

The solid content concentration of the lubrication coating solution is preferably 0.5% by mass or more, and more preferably 1% by mass or more, although this depends on the type of binder resin and solvent. The solid content concentration of the coating solution is preferably 35% by mass or less, and more preferably 20% by mass or less.

The drying temperature after coating is also preferable to be 70°C or higher, and preferably 250°C or lower, although this depends on the type of binder resin, the type of solvent, the presence or absence of a crosslinking agent, and the solid content concentration.

(Manufacturing of polyester film)
In the present invention, the polyester film that serves as the base film can be manufactured according to a general method for manufacturing polyester films. For example, one method involves melting polyester resin, extruding it into a sheet, stretching the unoriented polyester longitudinally using the speed difference of the rolls at a temperature above the glass transition temperature, then stretching it transversely using a tenter, and finally heat-treating it. Another method involves biaxial stretching simultaneously in both longitudinal and transverse directions within a tenter.

In this invention, the polyester film used as the base film may be either a uniaxially oriented film or a biaxially oriented film, but a biaxially oriented film is preferred.

The thickness of the polyester film substrate is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. A thickness of 5 μm or more is preferable because it reduces the likelihood of wrinkles forming during film transport.

The thickness of the polyester film substrate is preferably 50 μm or less, more preferably 45 μm or less, and even more preferably 40 μm or less. A thickness of 40 μm or less is preferable because it reduces the cost per unit area.

In the case of inline coating, the coating may be applied to the unstretched film before longitudinal stretching, or to the uniaxially oriented film after longitudinal stretching but before transverse stretching. When coating before longitudinal stretching, it is preferable to include a drying step before roll stretching. When coating the uniaxially oriented film before transverse stretching, the drying step can be combined with the film heating step in the tenter, so a separate drying step is not necessarily required. The same applies to simultaneous biaxial stretching.

The thickness of the smooth coating layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, even more preferably 0.02 μm or more, and particularly preferably 0.03 μm or more. A coating layer thickness of 0.001 μm or more is preferable because it maintains the film-forming properties of the coating film and allows for the acquisition of a uniform coating film.

The thickness of the smooth coating layer is preferably 2 μm or less, more preferably 1 μm or less, even more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. A coating layer thickness of 2 μm or less is preferable because it eliminates the risk of blocking.

The ceramic green sheet, which is coated and molded onto the release coating layer described later, is wound into a roll together with the release film after coating and molding. At this time, the release film's slip-free coating layer is in contact with the ceramic green sheet surface during winding. To prevent defects from occurring on the ceramic green sheet surface, the outer surface of the slip-free coating layer (the entire slip-free coating surface of the coated film that is not in contact with the polyester film) must be reasonably flat. Preferably, the average surface roughness (Sa) is between 1 nm and 25 nm, and the maximum protrusion height (P) is between 60 nm and 500 nm.

If the average surface roughness (Sa) of the outer surface of the easy-slip coating layer is 1 nm or more and the maximum protrusion height (P) is 60 nm or more, it is preferable because the easy-slip coating surface does not become too smooth and an appropriate level of slipperiness is maintained. If the average surface roughness (Sa) is 25 nm or less and the maximum protrusion height (P) is 500 nm or less, it is preferable because the easy-slip coating surface does not become too rough and defects in the ceramic green sheet due to protrusions do not occur.

In this invention, in addition to keeping the average surface roughness (Sa) and maximum protrusion height (P) within the above ranges, it is preferable that the average length of the roughness curve elements (RSm) is 10 μm or less. Controlling the average length of the roughness curve elements (RSm) to 10 μm or less increases the number of protrusions per unit area. An increase in the number of protrusions is preferable because it effectively suppresses the occurrence of pinholes, as the pressure applied to each protrusion is dispersed and reduced. More preferably, the average length of the roughness curve elements (RSm) is 5 μm or less, and even more preferably 3 μm or less. However, if the average length of the roughness curve elements (RSm) is too small, it is related to the excessive particle content in the smooth coating layer, and thus to an increase in the average surface roughness (Sa) and the maximum protrusion height (P). Therefore, it is preferable that it be 0.1 μm or more, but it may also be 0.5 μm or more, or even 1 μm or more.

In this invention, in order to set the average length (RSm) of the roughness curve elements within a predetermined range, the average particle size of the particles contained in the smooth coating layer is preferably 1000 nm or less. More preferably, it is 800 nm or less, and even more preferably, 600 nm or less. When the particle size is 1000 nm or less, the distance between particles does not become too large, and RSm is adjusted within the predetermined range, which is preferable. The surface free energy of the smooth coating layer is preferably 45 mJ/ ^m² or less, and more preferably 40 mJ/ ^m² or less. When the surface free energy of the smooth coating layer is 45 mJ/ ^m² or less, environmental foreign matter is less likely to adhere during the process, foreign matter adhesion to the release surface is less likely to occur, and pinholes caused by environmental foreign matter are less likely to occur in the ceramic green sheet, which is preferable.

(Release coating layer)
The resin constituting the release coating layer in the present invention is not particularly limited, and silicone resins, fluororesins, alkyd resins, various waxes, aliphatic olefins, etc., can be used, and each resin can be used alone or in combination of two or more types.

In this invention, the release coating layer can be, for example, a silicone resin, which is a resin having a silicone structure within its molecule. Examples include curable silicone, silicone graft resin, and modified silicone resins such as alkyl-modified resins. However, from the viewpoint of migration properties, it is preferable to use a reactive curable silicone resin. Reactive curable silicone resins can include those that undergo addition reactions, condensation reactions, or ultraviolet or electron beam curing. More preferably, low-temperature curable addition reaction resins and ultraviolet or electron beam curing resins are preferred. Using these allows for low-temperature processing during the coating process on polyester films. Therefore, thermal damage to the polyester film during processing is reduced, resulting in a highly flat polyester film, and minimizing defects such as pinholes during the production of ultrathin ceramic green sheets with a thickness of 0.2 to 2.0 μm.

Examples of silicone resins used in addition reactions include those obtained by reacting polydimethylsiloxane, which has vinyl groups introduced to its terminals or side chains, with hydrodienesiloxane using a platinum catalyst and curing the reaction. In this case, it is preferable to use a resin that can be cured at 120°C in 30 seconds or less, as this allows for processing at lower temperatures. Examples include low-temperature addition-curing types (LTC1006L, LTC1056L, LTC300B, LTC303E, LTC310, LTC314, LTC350G, LTC450A, LTC371G, LTC750A, LTC755, LTC760A, etc.) and thermal UV-curing types (LTC851, BY24-510, BY24-561, BY24-562, etc.) from Toray Dow Corning, as well as solvent addition + UV-curing types (X62-5040, X62-5065, X62-5072T, KS5508, etc.) and dual-cure curing types (X62-2835, X62-2834, X62-1980, etc.) from Shin-Etsu Chemical Co., Ltd.

Examples of silicone resins used in condensation reactions include those in which polydimethylsiloxane with OH groups at the ends and polydimethylsiloxane with H groups at the ends are condensed using an organotin catalyst to create a three-dimensional crosslinked structure.

Examples of UV-curable silicone resins include, as the most basic type, those that utilize the same radical reaction as conventional silicone rubber crosslinking, those that introduce unsaturated groups for photocuring, those that decompose onium salts with UV light to generate strong acids which then cleave epoxy groups for crosslinking, and those that crosslink through the addition reaction of thiols to vinylsiloxane. Furthermore, electron beams can be used instead of UV light. Electron beams have higher energy than UV light, and it is possible to carry out a radical crosslinking reaction without using an initiator, as is the case with UV curing. Examples of resins used include UV-curing silicones from Shin-Etsu Chemical Co., Ltd. (X62-7028A/B, X62-7052, X62-7205, X62-7622, X62-7629, X62-7660, etc.), UV-curing silicones from Momentive Performance Materials, Inc. (TPR6502, TPR6501, TPR6500, UV9300, UV9315, XS56-A2982, UV9430, etc.), and UV-curing silicones from Arakawa Chemical Corporation (Silicolise UV POLY200, POLY215, POLY201, KF-UV265AM, etc.).

As the UV-curing silicone resin mentioned above, acrylate-modified or glycidoxy-modified polydimethylsiloxane can also be used. Good mold release properties can also be achieved by mixing these modified polydimethylsiloxanes with polyfunctional acrylate resins or epoxy resins and using them in the presence of an initiator.

Other suitable resins include alkyd resins and acrylic resins that have undergone stearyl or lauryl modification, or alkyd resins and acrylic resins obtained by reactions such as methylated melamine.

Examples of aminoalkyd resins obtained through the reaction of methylated melamine include Tesfine 303, Tesfine 305, and Tesfine 314, manufactured by Hitachi Chemical Co., Ltd. Examples of aminoacrylic resins obtained through the reaction of methylated melamine include Tesfine 322, manufactured by Hitachi Chemical Co., Ltd.

When using the above-mentioned resin for the release coating layer in this invention, one type may be used, or two or more types may be mixed. Furthermore, additives such as light release additives and heavy release additives can be mixed in to adjust the release force.

The release coating layer in this invention may contain particles with a particle size of 1 μm or less, but from the viewpoint of pinhole generation, it is preferable to substantially omit any particles or other materials that form protrusions.

The release coating layer in this invention may contain additives such as adhesion enhancers and antistatic agents. Furthermore, to improve adhesion to the substrate, it is preferable to pre-treat the polyester film surface before applying the release coating layer, such as by applying an anchor coat, corona treatment, plasma treatment, or atmospheric pressure plasma treatment.

In this invention, the thickness of the release coating layer can be set according to its intended use and is not particularly limited, but preferably, the thickness of the release coating layer after curing is in the range of 0.005 to 2.0 μm. A thickness of 0.005 μm or more is preferable because it maintains release performance. Furthermore, a thickness of 2.0 μm or less is preferable because the curing time does not become excessively long, and there is no risk of uneven thickness in the ceramic green sheet due to a decrease in the flatness of the release film. Also, because the curing time is not excessively long, there is no risk of the resin constituting the release coating layer agglomerating and forming protrusions, thus reducing the likelihood of pinhole defects in the ceramic green sheet, which is preferable.

The outer surface of the film on which the release coating layer is formed (the entire surface of the release coating layer that is not in contact with the polyester film) should preferably be flat to prevent defects from occurring in the ceramic green sheet that is coated and molded on it. Preferably, the average surface roughness (Sa) is 5 nm or less and the maximum protrusion height (P) is 30 nm or less. Even more preferable is an average surface roughness of 5 nm or less and a maximum protrusion height of 20 nm or less. If the surface roughness is 5 nm or less and the maximum protrusion height is 30 nm or less, defects such as pinholes will not occur during the formation of the ceramic green sheet, resulting in a good yield, which is desirable. While a smaller average surface roughness (Sa) is preferable, it may be 0.1 nm or more, or 0.3 nm or more. Similarly, while a smaller maximum protrusion height (P) is preferable, it may be 1 nm or more, or 3 nm or more.

In this invention, in order to adjust the surface of the film on which the release coating layer is formed to a predetermined roughness range, it is preferable that the PET film is substantially free of inorganic particles. In this invention, "substantially free of inorganic particles" is defined as a quantitative analysis of elements derived from particles in both the base film and the release coating layer using X-ray fluorescence analysis, where the concentration is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit. This is because even without actively adding particles to the base film, contamination components originating from foreign matter, or dirt adhering to the raw material resin or the production lines and equipment during the film manufacturing process, can detach and become mixed into the film.

In this invention, the method for forming the release coating layer is not particularly limited. A coating solution containing a dissolved or dispersed release resin is applied to one side of a polyester film substrate. After removing the solvent by drying, the coating is then heated, heat-cured, or UV-cured. In this case, the drying temperature during solvent drying or heat curing is preferably 180°C or lower, more preferably 150°C or lower, and most preferably 120°C or lower. The heating time is preferably 30 seconds or less, and more preferably 20 seconds or less. A temperature of 180°C or lower is preferable because it maintains the flatness of the film and reduces the risk of thickness unevenness in the ceramic green sheet. A temperature of 120°C or lower is particularly preferable because it allows processing without impairing the flatness of the film and further reduces the risk of thickness unevenness in the ceramic green sheet.

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

In this invention, the coating liquid used when applying the release coating layer is not particularly limited, but it is preferable to add a solvent with a boiling point of 90°C or higher. Adding a solvent with a boiling point of 90°C or higher prevents bumping during drying, levels the coating film, and improves the smoothness of the coating film surface after drying. The amount added is preferably about 10 to 80% by mass of the total coating liquid.

Any known coating method can be applied to the above-mentioned coating solution. For example, conventional methods such as roll coating (including gravure coating and reverse coating), bar coating (including wire bar coating), die coating, spray coating, and air knife coating can be used.

(Ceramic green sheet and ceramic capacitor)
Generally, multilayer ceramic capacitors have a rectangular parallelepiped-shaped ceramic body. Inside the ceramic body, first internal electrodes and second internal electrodes are alternately arranged along the thickness direction. The first internal electrodes are exposed on the first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrodes are electrically connected to the first external electrode at the first end face. The second internal electrodes are exposed on the second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrodes are electrically connected to the second external electrode at the second end face.

The release film for manufacturing ceramic green sheets of the present invention is used to manufacture such multilayer ceramic capacitors. For example, it is manufactured as follows: First, the release film of the present invention is used as a carrier film, and a ceramic slurry for forming the ceramic substrate is applied and dried. A conductive layer for forming the first or second internal electrode is printed on the applied and dried ceramic green sheet. A mother laminate is obtained by appropriately laminating the ceramic green sheet, the ceramic green sheet with the conductive layer for the first internal electrode printed on it, and the ceramic green sheet with the conductive layer for the second internal electrode printed on it, and pressing them. The mother laminate is divided into multiple sections to produce raw ceramic substrates. Ceramic substrates are obtained by firing the raw ceramic substrates. Afterward, the multilayer ceramic capacitor can be completed by forming the first and second external electrodes.

Next, the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to the following examples. Furthermore, the evaluation methods used in the present invention are as follows.

[NMR measurement]
The ratio of copolymer components introduced into the acrylic polyol was confirmed using nuclear magnetic resonance spectroscopy ( ^1H -NMR, ^13C -NMR: Varian Unity 400, Agilent). The measurement was performed after removing the solvent from the synthesized acrylic polyol using a vacuum dryer, and then dissolving the dry material in deuterated chloroform. From the obtained NMR spectra, the chemical shift δ (ppm) peaks assigned to each group were identified. The integrated intensity of each peak was determined, and the composition ratio (mol%) of the copolymer components introduced into the acrylic polyol was confirmed from the number of hydrogen atoms at each group and the integrated intensity.

[Check Tg]
The Tg of each acrylic polyol was determined from the composition ratio of copolymer components obtained by the above NMR measurement and from the Fox formula described above.

[Suitability for extension]
To evaluate the stretchability of the acrylic polyol itself, synthesized acrylic polyols (1) to (13) were placed in a mixed solvent (25°C) of 30% by mass of isopropanol and 70% by mass of water to a solid content concentration of 12% by mass, to prepare a solution of the acrylic polyol alone. The solution was then applied to the surface of a polyester film that had been stretched only longitudinally using a Meyer bar #5. Next, the film sample with the applied layer (thickness 6.5 μm) was left to stand in a hot air circulating oven set at 60°C for 30 seconds, and then the film sample was removed from the oven for pre-drying. Next, the sample was set in a hand-cranked stretching device (manufactured by Toyobo Engineering Co., Ltd.) and placed in a hot air circulating oven at 100°C, where it was slowly stretched. The stretching operation was continued until the length was four times the length before stretching, and then the stretching device was removed from the hot air circulating oven. Subsequently, the stretched coating film was observed using an optical microscope (magnification: 200x), and the presence or absence of cracking due to stretching was determined according to the following criteria.
○: No cracks are visible at all.
△: Some cracks are visible (1 to 4).
×: Five or more cracks, or cracks are visible throughout the entire surface.

(1) Surface characteristics of the coated film The values were measured using a non-contact surface shape measurement system (VertScan R550H-M100) under the following conditions. The average surface roughness (Sa) and the average length of the roughness curve elements (RSm) were taken as the average of five measurements, and the maximum protrusion height (P) was taken as the maximum value of five measurements.

(Measurement conditions)
• Measurement mode: WAVE mode • Objective lens: 50x • 0.5x Tube lens • Measurement area: 187 x 139 μm² (Sa, P measurement)
• Measurement length (Lr: reference length): 187 μm (RSm measurement)
(2) Evaluation of particle dispersibility of the smooth coating layer (narrow field of view, VertScan measurement field of view 187 × 139 μm)
The value of the maximum protrusion height (P) measured in (1) above was judged according to the following criteria.

○: Maximum protrusion height (P) is 0.2 μm or less. ○△: Maximum protrusion height (P) is greater than 0.2 μm and less than 0.3 μm.

△: Maximum protrusion height (P) is 0.3 μm or more. (3) Evaluation of particle dispersibility of the slip-resistant coating layer (wide field of view, visual measurement field 600 mm x 420 mm)
In a darkroom, four A4-sized release films for green sheet manufacturing were observed visually using an LED light (LED LENSER P5R.2, manufactured by LED LENSER). White particle aggregates were marked and judged according to the following criteria.

◎: No particle aggregates ○: 1 to 3 particle aggregates.

△: Four or more particle aggregates are present.

(4) Powder shedding resistance A release film for green sheet manufacturing (3 cm (film width direction) x 20 cm (film length direction)) was mounted on a friction fastness tester (manufactured by Daiei Kagaku Seiki Seisakusho, RT-200) with the smooth coating layer facing upwards. An aluminum foil (thickness 80 μm, arithmetic mean surface roughness 0.03 μm) was used at the contact point between the load head (2 cm x 2 cm, 200 g) and the sample film, and the test was performed 10 times back and forth over a distance of 10 cm at a speed of 2 seconds per back and forth. The resulting film was placed on a black cardboard base and visually checked for powder shedding.

○: No powder fallout was observed on the black background.

△: Slight powder fallout is visible overall on the black background.

(5) Surface Free Energy Under conditions of 25°C and 50% RH, droplets of water (droplet volume 1.8 μL), diiodomethane (appropriate liquid volume 0.9 μL), and ethylene glycol (appropriate liquid 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), and the contact angles were measured. The contact angles were taken 10 seconds after each liquid was dropped onto the release film. The contact angle data for water, diiodomethane, and ethylene glycol obtained by the above method were calculated using the "Kitazaki-Hata" theory to determine the dispersion component γsd, polar component γsp, and hydrogen bonding component γsh of the surface free energy of the release film, and the sum of these components was taken as the surface free energy γs. This calculation was performed using the calculation software within the contact angle meter software (FAMAS).

(6) Charging during unwinding of release film rolls The release films for green sheet manufacturing obtained in each example and comparative example were wound into rolls with a width of 400 mm and a length of 5000 m to obtain release film rolls. After storing these release film rolls in an environment of 40°C and humidity of 50% or less for 30 days, the amount of charge when rewinding at 200 m/min was measured using a KSD-0103 manufactured by Kasuga Electric Co., Ltd. The amount of charge was measured at a point 100 mm immediately after unwinding, every 500 m of unwinding length, and the average value was calculated.

○: Less than ±3kV
○△: ±3kV or more, less than 5kV △: ±5kV or more, less than 10kV
×: ±10kV or more
(7) Evaluation of pinholes and thickness variation in ceramic green sheets A composition consisting of the following materials was stirred and mixed, and dispersed for 2 hours using a paint shaker with 2.0 mm glass beads as the dispersion medium to obtain a ceramic slurry.

Toluene 22.5% by mass
Ethanol 22.5% by mass
Barium titanate (HPBT-1, manufactured by Fuji Titanium Co., Ltd.) 50% by mass
Polyvinyl butyral (Sekisui Chemical Co., Ltd., Esrec BH-3) 5% by mass
Next, the release surface of the release film sample was coated with the dried slurry using an applicator to a thickness of 0.5 μm, dried at 90°C for 1 minute, the slurry surface and the smoothed coating surface were placed on top of each other, and a load of 1 kg/ ^cm² was applied for 10 minutes. After that, the release film was peeled off to obtain a ceramic green sheet.

In the central region of the obtained ceramic green sheet in the film width direction, light was shone from the opposite side of the surface coated with ceramic slurry over a 25 ^cm² area, and the occurrence of pinholes visible through the transmitted light was observed and visually judged according to the following criteria.

◎: No pinholes, excellent thickness variation ○: No pinholes, no particular problems with thickness variation △: Very few pinholes present, slight thickness variation visible.

×: There are some pinholes, and the thickness variation is somewhat noticeable.

(Preparation of polyethylene terephthalate pellets (PET(I)))
A continuous esterification reactor consisting of a three-stage complete mixing tank equipped with a stirrer, a partial condenser, a raw material inlet, and a product outlet was used as the esterification reactor. Terephthalic acid (TPA) was supplied at a rate of 2 tons/hour, ethylene glycol (EG) at a ratio of 2 moles per mole of TPA, and antimony trioxide was added in an amount that resulted in 160 ppm of Sb atoms relative to the generated PET. This slurry was continuously supplied to the first esterification reactor of the esterification reactor and reacted at atmospheric pressure at 255°C for an average residence time of 4 hours. Next, the reaction product in the first esterification reactor was continuously removed from the system and supplied to the second esterification reactor. EG distilled off from the first esterification reactor was supplied to the second esterification reactor at a concentration of 8% by mass relative to the generated PET. Furthermore, an EG solution containing magnesium acetate tetrahydrate in an amount that resulted in 65 ppm of Mg atoms relative to the generated PET, and an EG solution containing TMPA (trimethyl phosphate) in an amount that resulted in 40 ppm of P atoms relative to the generated PET were added, and the reaction was carried out at atmospheric pressure at 260°C for an average residence time of 1 hour. Next, the reaction products from the second esterification reactor were continuously removed from the system and supplied to the third esterification reactor. Using a high-pressure disperser (manufactured by Nippon Seiki Co., Ltd.), 0.2% by mass of porous colloidal silica with an average particle size of 0.9 μm, which had been dispersed at a pressure of 39 MPa (400 kg/ ^cm² ) for an average of 5 passes, and 0.4% by mass of synthetic calcium carbonate with an average particle size of 0.6 μm, which had 1% by mass of polyacrylic acid ammonium salt attached to calcium carbonate, were added as 10% EG slurry each, and the mixture was reacted at atmospheric pressure at 260°C for an average residence time of 0.5 hours. The esterification reaction product generated in the third esterification reaction vessel was continuously supplied to a three-stage continuous polycondensation reactor for polycondensation. The product was filtered through a filter made of sintered stainless steel fibers with a 95% cut diameter of 20 μm, then ultrafiltration was performed, and the product was extruded into water. After cooling, it was cut into chips to obtain PET chips with an intrinsic viscosity of 0.60 dl/g (hereinafter abbreviated 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 production of the above-mentioned PET chip, a PET chip with an intrinsic viscosity of 0.62 dl/g that does not contain any particles such as calcium carbonate or silica was obtained (hereinafter abbreviated as PET(II)).

(Manufacturing of laminated film Z)
After drying, these PET chips were melted at 285°C and then melted again at 290°C in a separate extruder. A two-stage filtration process was performed 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 then combined in a feed block, and PET(I) was laminated as the anti-release side layer and PET(II) as the release side layer. The sheet was extruded (casted) at a speed of 45 m/min and electrostatically adhered and cooled on a casting drum at 30°C using the electrostatic adhesion method to obtain an unstretched polyethylene terephthalate sheet with an intrinsic viscosity of 0.59 dl/g. The layer ratio was adjusted so that PET(I)/(II) = 60%/40% based on the discharge rate calculations 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. Subsequently, the material was guided into a tenter and stretched 4.2 times laterally at 140°C. Next, it was heat-treated at 210°C in a heat-fixing zone. After that, a 2.3% relaxation treatment was performed laterally at 170°C to obtain a biaxially oriented polyethylene terephthalate film Z with a thickness of 31 μm. The Sa of the obtained film Z was 2 nm in the release side layer and 28 nm in the non-release side layer.

(Manufacturing of Acrylic Polyol A-1)
A four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet was charged with 77 parts by mass of methyl methacrylate (MMA), 100 parts by mass of hydroxyethyl methacrylate (HEMA), 33 parts by mass of methacrylic acid (MAA), and 490 parts by mass of isopropyl alcohol (IPA). The flask was heated to 80°C while stirring. The flask was stirred for 3 hours while maintaining the temperature at 80°C, after which 0.5 parts by mass of 2,2-azobis-2-methyl-N-2-hydroxyethylpropionamide was added to the flask. The flask was heated to 120°C while purging with nitrogen, and the mixture was stirred at 120°C for 2 hours.
Next, the mixture was subjected to a reduced pressure of 1.5 kPa at 120°C to remove unreacted raw materials and solvent, yielding an acrylic polyol. The flask was returned to atmospheric pressure and cooled to room temperature, and 840 parts by mass of an IPA aqueous solution (water content 50% by mass) was added and mixed. Then, while stirring, triethylamine was added using a dropping funnel, and the acrylic polyol was neutralized until the pH of the solution was in the range of 5.5 to 7.5, yielding an acrylic polyol (A-1) with a solid content of 20% by mass. The composition ratio, Tg, stretchability, and acid value of acrylic polyol (A-1) as determined by NMR are shown in Table 1.

(Manufacturing of acrylic polyols (A-2) to (A-13))
As shown in Table 1, acrylic polyols (A-2) to (A-13) with a solid content of 20% by mass were obtained in the same manner as in the production of acrylic polyol 1, except that the amounts of MMA, St, SMA, HEMA, MAA, AA, IPA at the time of charging, IPA aqueous solution at the time of dilution, and neutralizing agent were changed. The composition ratio, Tg, stretchability, acid value, and hydroxyl value of acrylic polyols (A-2) to (A-13) as determined by NMR measurement are also shown in Table 1. The composition ratio is expressed as l-1, l-2, and l-3 (units) for MMA, St (styrene), and SMA (stearyl methacrylate), respectively, m (unit) for HEMA, and n (unit) for MAA and AA (acrylic acid).

(Polymerization of polyester resin B0-1)
In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate, 185.1 parts by mass of ethylene glycol, 185.1 parts by mass of neopentyl glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was carried out at a temperature of 160°C to 220°C for 4 hours. The temperature was then raised to 255°C, the reaction system was gradually depressurized, and the reaction was carried out under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain copolymerized polyester resin (B0-1). The obtained copolymerized polyester resin (B0-1) was pale yellow and transparent. The reduced viscosity of copolymerized polyester resin (B0-1) was measured to be 0.60 dl/g. The glass transition temperature determined by DSC was 65°C.

(Manufacturing of polyester aqueous dispersion B-1)
In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of polyester resin (B0-1) and 15 parts by mass of ethylene glycol-n-butyl ether were added and heated at 110°C, stirring to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester aqueous dispersion (B-1) with a solid content of 30% by mass.

(Polymerization of polyester resin B0-2)
A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 163 parts by mass of dimethyl terephthalate, 163 parts by mass of dimethyl isophthalate, 169 parts by mass of 1,4-butanediol, 324 parts by mass of ethylene glycol, and 0.5 parts by mass of tetra-n-butyl titanate, and the transesterification reaction was carried out at a temperature of 160°C to 220°C for 4 hours.

Next, 14 parts by mass of fumaric acid and 203 parts by mass of sebacic acid were added, and the temperature was raised from 200°C to 220°C over 1 hour to carry out the esterification reaction. Then, the temperature was raised to 255°C, the reaction system was gradually reduced in pressure, and the reaction was carried out under a reduced pressure of 29 Pa for 1 hour and 30 minutes to obtain a hydrophobic copolymer polyester resin (B0-2). The obtained hydrophobic copolymer polyester resin (B0-2) was pale yellow and transparent.

(Manufacturing of polyester aqueous dispersion B-2)
Next, 60 parts by mass of the copolymerized polyester resin (B0-2), 45 parts by mass of methyl ethyl ketone, and 15 parts by mass of isopropyl alcohol were placed in a reactor equipped with a graft resin production stirrer, thermometer, reflux device, and quantitative dropper, and the mixture was heated and stirred at 65°C to dissolve the resin. After the resin was completely dissolved, 24 parts by mass of maleic anhydride was added to the polyester solution.

Next, a solution prepared by dissolving 16 parts by mass of styrene and 1.5 parts by mass of azobisdimethylvaleronitrile in 19 parts by mass of methyl ethyl ketone was added dropwise to the polyester solution at a rate of 0.1 ml/min, and stirring was continued for 2 hours. After sampling the reaction solution for analysis, 8 parts by mass of methanol was added. Then, 300 parts by mass of water and 24 parts by mass of triethylamine were added to the reaction solution, and stirring was continued for 1 hour.

Subsequently, the reactor temperature was raised to 100°C, and methyl ethyl ketone, isopropyl alcohol, and excess triethylamine were removed by distillation to obtain a pale yellow, transparent polyester resin. A homogeneous, water-dispersible polyester graft copolymer dispersion (B-2) with a solid content of 25% by mass was then prepared. The glass transition temperature of the obtained polyester graft copolymer was 68°C.

(Manufacturing of polyurethane aqueous dispersion C-1)
In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 43.75 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, 153.41 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred at 75°C under a nitrogen atmosphere for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, the reaction solution was cooled to 40°C, and then 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, in a reaction vessel equipped with a homodisperser capable of high-speed stirring, 450 g of water was added, the temperature was adjusted to 25°C, and the polyurethane prepolymer solution was added and dispersed in water while stirring at 2000 ^min⁻¹ . Subsequently, a water-soluble polyurethane resin solution C-1 with a solid content of 37% by mass was prepared by removing some of the acetone and water under reduced pressure. The glass transition temperature of the obtained polyurethane resin was -30°C.

(Melamine-based crosslinking agent D-1)
Methylated melamine (manufactured by Sanwa Chemical, product name Nikalac MX-035, solid content concentration 70% by mass)
(Melamine-based crosslinking agent D-2)
Methyl/n-butylated melamine (manufactured by Sanwa Chemical, trade name Nikalac MX-45, solid content concentration 100% by mass)
(Silica particles E-1)
Colloidal silica (manufactured by Nissan Chemical Corporation, product name MP2040, average particle size 200 nm, solid content concentration 40% by mass)
(Silica particles E-2)
Colloidal silica (manufactured by Nissan Chemical Corporation, product name Snowtex XL, average particle size 40 nm, solid content concentration 40% by mass)
(Silica particles E-3)
Colloidal silica (manufactured by Nissan Chemical Corporation, trade name Snowtex ZL, average particle size 100 nm, solid content concentration 40% by mass)
(Silica particles E-4)
Colloidal silica (manufactured by Nissan Chemical Corporation, trade name MP4540M, average particle size 450 nm, solid content concentration 40% by mass)
(Acrylic particles E-5)
Acrylic particle aqueous dispersion (manufactured by Nippon Shokubai, product name MX100W, average particle size 150 nm, solid content concentration 10% by mass)
(Acrylic particles E-6)
Acrylic particle aqueous dispersion (manufactured by Nippon Shokubai, product name MX200W, average particle size 350 nm, solid content concentration 10% by mass)
(Acrylic particles E-7)
Acrylic particle aqueous dispersion (manufactured by Nippon Shokubai, product name MX300W, average particle size 450 nm, solid content concentration 10% by mass)
(Release agent solution X-1)
A release agent solution with a solid content of 2% by mass was prepared by diluting 100 parts by mass of thermosetting amino alkyd resin (Tesfine 314, manufactured by Hitachi Chemical Co., Ltd., 60% by mass of solids) and 1.2 parts by mass of p-toluenesulfonic acid (Dryer 900, manufactured by Hitachi Chemical Co., Ltd., 50% by mass of solids) as a curing catalyst with a toluene/methyl ethyl ketone/heptane (=3:5:2) solution.

(Release agent solution X-2)
A mold release agent solution with a solid content of 2% by mass was prepared by diluting 100 parts by mass of UV-curable silicone resin (Momentive UV9300, solid content concentration 100% by mass) and 1 part by mass of curing catalyst bis(alkylphenyl)iodonium hexafluoroantimonate with a toluene/methyl ethyl ketone/heptane (=3:5:2) solution.

(Example 1)
(Preparation of lubrication solution 1)
A lubricating coating solution 1 with the following composition was prepared.

(Smooth coating liquid 1)
Water 45.51 parts by mass, Isopropyl alcohol 35.00 parts by mass, Acrylic polyol resin A-1 (solid content concentration 20% by mass) 16.57 parts by mass, Melamine-based crosslinking agent D-1 (solid content concentration 70% by mass) 2.03 parts by mass, Silica particles E-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Surfactant F-1 (silicone-based, solid content concentration 10% by mass) 0.30 parts by mass (for the manufacture of polyester film)
As a film raw material polymer, PET resin pellets (PET(II)) with an intrinsic viscosity (solvent: phenol/tetrachloroethane = 60/40) of 0.62 dl/g and substantially free of particles were dried at 135°C for 6 hours under a reduced pressure of 133 Pa. The pellets were then fed into an extruder and melt-extruded into a sheet at approximately 280°C. The sheet was then rapidly cooled and solidified on a rotating, cooled metal roll maintained at a surface temperature of 20°C to obtain an unstretched PET sheet.

This unstretched PET sheet was heated to 100°C using a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction using a roll group with different peripheral speeds to obtain a uniaxially oriented PET film.

Next, the above-mentioned lubrication solution was applied to one side of the PET film using a bar coater and dried at 80°C for 15 seconds. The coating thickness was adjusted to 0.1 μm after final stretching and drying. Subsequently, the film was stretched 4.0 times in the width direction at 150°C using a tenter. With the film's width direction length fixed, it was heated at 230°C for 0.5 seconds, and then subjected to a 3% widthwise relaxation treatment at 230°C for 10 seconds to obtain an in-line coated polyester film with a thickness of 31 μm.

(Formation of release coating layer)
The in-line coated polyester film obtained above was coated with release agent solution X-1 on the surface opposite to the laminated surface of the easy-slip coating layer using a reverse gravure coater to a thickness of 0.1 μm after drying. Then, it was dried with hot air at 130°C for 30 seconds to form a release coating layer and obtain a release film for manufacturing ultrathin ceramic green sheets. Winding properties, process passability, and handling properties were excellent with no particular problems. After winding as a roll, the electrostatic charge when unwinding again for ceramic sheet coating was low, suppressing the adhesion of environmental foreign matter, and enabling the production of high-quality ceramic capacitors without reducing the yield of ceramic capacitors.

(Example 2)
A release film for manufacturing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that a release film for manufacturing an ultrathin ceramic green sheet was used the release film for manufacturing an ultrathin ceramic green sheet was used in the same manner as in Example

(Examples 3-19, 21-24)
A polyester film was obtained in the same manner as in Example 1, except that the lubrication coating liquid 1 was changed as shown in Table 2.

(Example 20)
A release film for manufacturing an ultrathin ceramic green sheet was obtained in the same manner as in Example 1, except that the release coating layer was formed as described below.

(Formation of release coating layer)
The obtained inline coated polyester film was coated with release agent solution X-2 using a reverse gravure coater to a thickness of 0.1 μm after drying. Then, it was dried with hot air at 90°C for 30 seconds, and immediately afterward, ultraviolet irradiation (300 mJ/cm2) was performed using an electrodeless lamp (H bulb manufactured by Heraeus Corporation) to form a release coating layer and obtain a release film for manufacturing ultrathin ceramic green sheets.

(Comparative Examples 1-4)
A polyester film was obtained in the same manner as in Example 1, except that the lubrication coating liquid 1 was changed as shown in Table 2.

(Comparative Example 5)
A release film for manufacturing ceramic green sheets was obtained in the same manner as in Example 1, except that E5000-25μm (manufactured by Toyobo) was used as the film for forming the release coating layer, instead of the inline coating film with an easy-slip coating layer on one surface prepared in Example 1. E5000 contained particles inside the film, and the Sa on both surfaces was 0.031μm.

(Comparative Example 6)
A release film for manufacturing ceramic green sheets was obtained in the same manner as in Example 1, except that the inline coating film prepared in Example 1, which had a smooth coating layer on one surface, was replaced with a laminated film Z as the film for forming the release coating layer. The release coating layer was applied to the surface of the laminated film Z from which the PET(II) pellets were ejected (the layer that does not contain particles).

The evaluation results for each example and comparative example are shown in Table 2.

In Table 2 above, the composition of the resin, crosslinking agent, particles, and surfactant in the lubrication solution is listed as parts by mass of solids. The sum of the parts by mass of solids of the resin, crosslinking agent, particles, and surfactant present in the lubrication solution represents the total parts by mass of solids in the lubrication layer. The mass percentage of each component (resin, crosslinking agent, particles, and surfactant) in the total solids of the lubrication layer can be determined by dividing its respective parts by mass by the total parts by mass of solids in the lubrication layer.

In Examples 1 to 24, the discharge charge was low when the roll was unwound again after the release process, and environmental contaminants were less likely to adhere. Therefore, it was possible to produce high-quality ceramic capacitors without reducing the yield of ceramic capacitors. The release film used was a polyester film that substantially did not contain inorganic particles as the base material. The base material had a release coating layer on one surface and a slip-free coating layer containing particles on the other surface. Since the slip-free coating layer was formed by curing a composition containing acrylic resin and a melamine-based crosslinking agent, the crosslinking density of the slip-free coating layer was high, resulting in a small amount of deformation of the slip-free coating layer. It is believed that the amount of discharge was suppressed because the contact area between the release layer and the slip-free layer was reduced when unwinding the release-processed film roll.

On the other hand, in Comparative Examples 1 to 4, since the easy-slip coating layer was not formed by curing a composition containing the acrylic resin and melamine-based crosslinking agent specified in the present invention, the crosslinking density of the easy-slip coating layer was low, and the amount of deformation of the easy-slip coating layer was large. It is thought that the discharge charge increased because the contact area between the release layer and the easy-slip layer increased when the release-processed film roll was unwound. Furthermore, although the discharge charge was low in Comparative Examples 5 and 6, they lacked the easy-slip coating layer specified in the present invention, and the surface roughness of the easy-slip surface was large, resulting in the occurrence of pinholes in the ceramic sheet.

According to the present invention, it is possible to provide a release film for manufacturing ceramic green sheets that can simultaneously prevent pinholes and localized thickness variations, as well as prevent the adhesion of environmental foreign matter due to static electricity, even when the ceramic green sheet is made into a thin film. Furthermore, by using the release film for manufacturing ceramic green sheets of the present invention, an ultra-thin ceramic green sheet can be obtained, enabling the efficient manufacture of minute ceramic capacitors.

Claims (5)

Using polyester film as the base material,
The substrate has a release coating layer on one surface and a smooth coating layer containing particles on the other surface.
When elements originating from inorganic particles were quantitatively analyzed by X-ray fluorescence analysis of both the base film and the release coating layer, the concentration was 50 ppm or less.
The aforementioned smooth coating layer is formed by curing a composition containing an acrylic resin, a crosslinking agent , and a surfactant .
The aforementioned crosslinking agent is a melamine-based crosslinking agent.
A release film for manufacturing ceramic green sheets, wherein the hydroxyl value of the acrylic resin is 50 mg KOH/g or more and 450 mg KOH/g or less. The release film for manufacturing ceramic green sheets according to claim 1, wherein the glass transition temperature of the acrylic resin is 50°C or higher and 110°C or lower. The release film for manufacturing ceramic green sheets according to claim 1, wherein the average surface roughness (Sa) of the slip-free coating layer is 1 nm to 25 nm, the maximum protrusion height (P) is 60 nm to 500 nm, and the average length (RSm) of the roughness curve elements is 10 μm or less. The release film for manufacturing ceramic green sheets according to claim 1, wherein the thickness of the slip-free coating layer is 0.001 μm or more and 2 μm or less. A polyester film that substantially does not contain inorganic particles is used as the base material.
The substrate has a release coating layer on one surface and a smooth coating layer containing particles on the other surface.
The aforementioned smooth coating layer is formed by curing a composition containing an acrylic resin, a crosslinking agent, and a surfactant.
The aforementioned crosslinking agent is a melamine-based crosslinking agent.
A release film for manufacturing ceramic green sheets, wherein the hydroxyl value of the acrylic resin is 50 mg KOH/g or more and 450 mg KOH/g or less.