JP7842966B2 - Release film - Google Patents

Description

This invention relates to a release film having a base film and a release layer, and more particularly to a release film useful as a film for various processes.

Conventionally, release films based on polyester films and the like have high heat resistance and mechanical properties, and are used as process films for manufacturing adhesive sheets, cover films, and resin sheets such as ceramic slurries and polymer electrolyte membranes. Furthermore, many release layers formed from silicone-containing coating compositions have been proposed for release films due to their good heat resistance and release properties (for example, Patent Documents 1-4).

Patent documents 1 and 2 propose release films in which a release layer is formed using a coating composition containing a polysiloxane having an unsaturated group, a polysiloxane having a Si-H group, a platinum group metal catalyst, and an organic solvent.

However, this technology had a problem: because it resulted in an organic solvent-based coating composition, it was unsuitable for application during the stretching and film formation of a substrate film (hereinafter referred to as "in-line coating"). In other words, because an organic solvent was used alone as the solvent for the coating composition, the film formation and stretching equipment required extensive explosion-proof equipment, resulting in high initial installation costs and complicated operation, thus increasing manufacturing costs.

On the other hand, as a technology suitable for in-line coating, Patent Document 3 proposes a release film in which a release layer is formed using an aqueous coating composition containing an alkenyl group-containing silicone and a Si-H group-containing silicone. Furthermore, as an example, a release film is disclosed in which a release layer is formed using an alkenyl group-containing silicone with a number average molecular weight of 25,000 and a Si-H group-containing silicone with a number average molecular weight of 4,500.
Furthermore, Patent Document 4 proposes a release film in which a release layer is formed using an aqueous coating composition containing an alkenyl group-containing silicone having Q units represented by SiO₄ _/2 and an Si-H group-containing silicone, for the purpose of achieving both easy release and good wettability. In addition, as an example, a release film is disclosed in which a release layer is formed using an alkenyl group-containing silicone with a number average molecular weight of 25,000 having Q units and an Si-H group-containing silicone with a number average molecular weight of 4,500.

Thus, conventionally, when forming a release layer, relatively high molecular weight polysiloxanes containing unsaturated groups were generally used to facilitate the formation of the polydimethylsiloxane helical structure on the coating surface. This was also true when using organic solvent-based coating compositions (for example, Patent Documents 1-2).

Japanese Patent Publication No. 2003-292894 Japanese Patent Publication No. 2003-292895 Patent No. 6077327 Japanese Patent Publication No. 2021-11081 International Public Gazette WO2017/200056

However, in recent years, there has been a trend towards thinner ceramic green sheets and other materials formed on the release layer of release films. The surface of the release layer is sometimes required to have both release properties and wettability to ceramic slurries, and achieving both is becoming difficult. In other words, changing the chemical composition of the release layer to improve wettability leads to a decrease in release properties.

Furthermore, Patent Document 5 proposes a release film having a release layer using an organic solvent-based coating composition containing polydimethylsiloxane having vinyl groups with a molecular weight of 500 to 30,000 and polydimethylsiloxane having Si-H groups with a molecular weight of 150 to 10,000. However, it does not suggest achieving both release properties and wettability, and it has the problem of being unsuitable for in-line coating due to its organic solvent base.

Furthermore, our investigations revealed that when silicone-based release films are recycled and used as raw materials for base films, depending on the composition of the release layer, foreign matter exceeding a certain size may be generated, making them unsuitable for recycling.

Furthermore, according to another study by the present inventors, when forming a release layer using a silicone-based aqueous coating composition, it was found that the influence of aggregates generated during the application of the release layer on the surface shape tends to be a problem when dealing with thin films such as ceramic green sheets.

Therefore, the object of the present invention is to provide a release film that easily achieves both release properties and wettability of the release layer, and has good coating uniformity and recyclability of the release layer.

The inventors of this invention, after diligent research to solve the aforementioned problems, discovered that the above problems can be solved by forming a release layer using an aqueous coating composition with a lower molecular weight silicone than conventional methods, and thus completed the present invention. That is, the present invention includes the following:

[1] A release film having a base film and a release layer formed by reacting and solidifying an aqueous coating composition,
The aqueous coating composition comprises an alkenyl group-containing silicone having two or more alkenyl groups and Q units represented by SiO₄ _/2 in its molecule, with a number average molecular weight of 1,000 or more and less than 10,000, and an Si-H group-containing silicone having two or more Si-H groups in its molecule, with a number average molecular weight of 1,000 or more and less than 5,000, and a mold release film.

[2] The release film according to [1], wherein the alkenyl group-containing silicone is represented by the following general formula (I).

(In general formula (I), ^R1 may be the same or different alkenyl group having 2 to 8 carbon atoms, or a monovalent hydrocarbon group having 1 to 16 carbon atoms including an alkyl group or aryl group, and one or more of the ^R1s bonded to the silicon atom represented by [SiO] _b1 are alkenyl groups having 2 to 8 carbon atoms, ^R2 may be the same or different monovalent hydrocarbon group having 1 to 16 carbon atoms including an alkyl group or aryl group, and ^Y1 may be the same or different represented by general formula (Ia).

(In general formula (Ia), ^R1 is the same as ^R1 in general formula (I), and may be identical or different.)
In the entire general formula (I) containing ^Y1 , when all silicon atoms, including terminal atoms, are considered to be 100 mol%, a1 is between 50 mol% and 98 mol%, b1 is between 0 mol% and 10 mol%, c1 is between 0.5 mol% and 30 mol%, and d1 is between 0 mol% and 50 mol%. In the entire general formula (I) containing ^Y1 , two or more of ^R1 are alkenyl groups having 2 to 8 carbon atoms.

[3] The release film according to [1] or [2], wherein the Si-H group-containing silicone is represented by the following general formula (II).

(In general formula (II), ^R3 is a monovalent hydrocarbon group having 1 to 16 carbon atoms, which may be the same or different alkyl or aryl group, and when a2 + b2 is 100 mol%, a2 is 30 mol% to 90 mol%, and b2 is 10 mol% to 70 mol%.)

[4] The release film according to any one of [1] to [3], wherein the aqueous coating composition comprises 1 to 50 parts by mass of the Si-H group-containing silicone per 100 parts by mass of the alkenyl group-containing silicone.

[5] The release layer is formed by applying the aqueous coating composition to a substrate film before crystal orientation is completed, stretching it in at least one direction, and then heat-treating it to complete the crystal orientation, according to any one of items [1] to [4].

[6] The release film according to any one of items [1] to [5], wherein the base film is a polyester film.

[7] The release film according to any one of items [1] to [6], wherein the release film is a release film for multilayer ceramic capacitors or a release film for resin sheets.

According to the present invention, it is possible to provide a release film that easily achieves both release properties and wettability of the release layer, and has good coating uniformity and recyclability of the release layer.

While the exact reasons for these effects are unclear, it is believed that silicone crosslinks formed by the reaction of relatively low molecular weight silicones readily form dense three-dimensional structures. This allows them to maintain their hardness even in contact with organic solvents, reducing the adhesion force required when peeling laminates coated or cast onto the release layer surface. Furthermore, silicone crosslinks with dense three-dimensional structures are less likely to form helical structures such as those of polydimethylsiloxane. This affects the surface free energy of the release layer surface, making it easier to achieve appropriate wettability for the laminate. In particular, the presence of Q units in alkenyl group-containing silicones facilitates the formation of dense three-dimensional structures, making it easier to achieve both release and wettability in the release layer.

Furthermore, by reducing the molecular weight of the silicone contained in the aqueous coating composition, the stability and uniformity of the coating film are increased, making it less likely for aggregates to form in the release layer, thus improving coating uniformity. Also, during remelting for recycling, the highly uniform coating film is more easily dispersed within the remelted base film resin, thus reducing the likelihood of foreign matter formation.

The present invention will be described in detail below.

[Release film]
The release film of the present invention comprises a base film (hereinafter sometimes referred to as "base") and a release layer formed by reacting and solidifying an aqueous coating composition. As will be described in detail later, the aqueous coating composition contains two types of silicones that can react with each other, so identifying the structure of the resulting polymer and specifying claims based thereon is not easy and impractical. For this reason, the release film of the present invention is specified in the form of a product-by-process claim.

[Release layer]
The release layer is obtained by reacting and solidifying the aqueous coating composition. The aqueous coating composition contains an alkenyl group-containing silicone having two or more alkenyl groups and Q units represented by SiO₄ _/2 in its molecule, with a number average molecular weight of 1,000 to less than 10,000, and an Si-H group-containing silicone having two or more Si-H groups in its molecule, with a number average molecular weight of 1,000 to 5,000. The components will be described in detail below.

(Alkenyl group-containing silicone)
The alkenyl group-containing silicone can be any compound having two or more alkenyl groups and a Q unit represented by SiO₄ _/2 in its molecule, and having a siloxane bond in its main chain, but polyorganosiloxanes having alkenyl groups at the terminals and/or side chains are preferred. Furthermore, copolymers containing dialkylsiloxane units or alkylphenylsiloxane units are preferred because they allow for easy adjustment of the amount of alkenyl groups in one molecule while exhibiting peelability. The terminal silicon atoms preferably have alkenyl groups, but they may also have a trialkylsilane structure such as trimethylsilane.

The alkenyl group may be introduced at one end, both ends, or on the side chain, but it is preferable that it be introduced at least at one end, and more preferably at both ends of the main chain. The molecule contains two or more alkenyl groups, preferably between 2 and 20, and more preferably between 2 and 10.

The Q unit content, represented as SiO₄ _/2 , is preferably 0.5 mol% to 30 mol%, and more preferably 0.5 mol% to 20 mol%, when all silicon atoms, including terminal atoms, within the molecule are considered to be 100 mol%. When the Q unit content is 0.5 mol% or more, it becomes easier to form a dense release layer with high cohesive force, making it easier to achieve both release properties and wettability in the release layer. When the Q unit content is 30 mol% or less, it becomes easier to suppress the formation of an overly dense structure, thereby preventing the coating film from becoming brittle.
Examples of alkenyl group-containing silicones include organopolysiloxanes represented by the following general formula (I).

(In general formula (I), ^R1 may be the same or different alkenyl group having 2 to 8 carbon atoms, or a monovalent hydrocarbon group having 1 to 16 carbon atoms including an alkyl group or aryl group, and one or more of the ^R1s bonded to the silicon atom represented by [SiO] _b1 are alkenyl groups having 2 to 8 carbon atoms, ^R2 may be the same or different monovalent hydrocarbon group having 1 to 16 carbon atoms including an alkyl group or aryl group, and ^Y1 may be the same or different represented by general formula (Ia).

(In general formula (Ia), ^R1 is the same as ^R1 in general formula (I), and may be identical or different.)
In the entire general formula (I) containing ^Y1 , when all silicon atoms, including terminal atoms, are considered to be 100 mol%, a1 is between 50 mol% and 98 mol%, b1 is between 0 mol% and 10 mol%, c1 is between 0.5 mol% and 30 mol%, and d1 is between 0 mol% and 50 mol%. In the entire general formula (I) containing ^Y1 , two or more of ^R1 are alkenyl groups having 2 to 8 carbon atoms.
The ^R2 bonded to the silicon atom indicated by [SiO] _a1 may be a monovalent hydrocarbon group containing an alkyl group or an aryl group, but it is preferably a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from alkyl groups or aryl groups, more preferably a methyl group or a phenyl group, and even more preferably a methyl group.

The ^R1 bonded to the silicon atom indicated by [SiO] _b1 is a monovalent hydrocarbon group containing an alkenyl group having 2 to 8 carbon atoms, or an alkyl group or aryl group. One or more of these groups may be alkenyl groups having 2 to 8 carbon atoms, but it is preferable that R1 be a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from alkenyl groups having 2 to 8 carbon atoms, or alkyl groups or aryl groups. If ^R1 is a hydrocarbon group other than an alkenyl group, a methyl group or a phenyl group is more preferable, and a methyl group is even more preferable.
The ^R1 bonded to the silicon atom indicated by [SiO] _d1 may be a monovalent hydrocarbon group containing an alkenyl group having 2 to 8 carbon atoms, or an alkyl or aryl group. Preferably, it is a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from an alkenyl group having 2 to 8 carbon atoms, or an alkyl or aryl group, and more preferably a monovalent hydrocarbon group having 1 to 16 carbon atoms selected from an alkyl or aryl group. If ^R1 is a hydrocarbon group other than an alkenyl group, a methyl group or a phenyl group is more preferable, and a methyl group is even more preferable.

The ^R1 groups at both ends of the main chain are similar to the ^R1 groups bonded to silicon atoms in [SiO] _b1 , but a preferred configuration is an alkenyl group having 2 to 8 carbon atoms. Terminal alkenyl groups are particularly preferred because they result in relatively small steric hindrance when reacting with Si-H groups, thus improving exfoliation.
The ^R1 bonded to the terminal silicon atom in general formula (Ia) is similar to the ^R1 bonded to the silicon atom shown in [SiO] _b1 , but a preferred configuration is an alkenyl group having 2 to 8 carbon atoms, as this densifies the crosslinking structure, improves the cohesive force of the release layer, and improves the release properties of process materials, such as those mediated by organic solvents.

Examples of alkenyl groups with 2 to 8 carbon atoms represented by ^R1 include vinyl groups, allyl groups, butenyl groups, pentenyl groups, and hexenyl groups, with vinyl groups being particularly preferred among these.

In the general formula (I) including ^Y1 , when all silicon atoms, including terminal atoms, are considered to be 100 mol%, a1 is 50 mol% or more and 98 mol% or less, but 70 mol% or more and 98 mol% or less is preferred. Also, b1 is 0 mol% or more and 10 mol% or less, but 0 mol% or more and 5 mol% or less is preferred. c1 is 0.5 mol% or more and 30 mol% or less, but 0.5 mol% or more and 20 mol% or less is preferred. d1 is 0 mol% or more and 50 mol% or less, but 0 mol% or more and 30 mol% or less is preferred.
When the total amount of constituent units of [SiO] _a1 and [SiO] _b1 is 100 mol%, from the viewpoint of localizing hydrocarbon groups on the coating surface in order to improve peelability, the range of constituent units of [SiO] _a1 is preferably 90 mol% to 100 mol%, and more preferably 95 mol% to 100 mol%.

The number-average molecular weight of alkenyl group-containing silicones is preferably 1,000 or more and less than 10,000, more preferably 3,000 or more and less than 10,000. If the number-average molecular weight is less than 1,000, the hydrocarbon groups tend to localize on the coating surface, making it easier to obtain sufficient peelability. On the other hand, if the number-average molecular weight is less than 10,000, the emulsification properties in water-based coating compositions tend to be good, and uniform coating properties also tend to be good.

(Si-H group-containing silicone)
As the Si-H group-containing silicone, any compound having two or more Si-H groups (i.e., two or more hydrogen atoms directly bonded to a Si atom) in the molecule and a siloxane bond in the main chain is acceptable, but polyorganosiloxanes having Si-H groups in the side chains are preferred. Furthermore, copolymers containing dialkylsiloxane units or alkylphenylsiloxane units are preferred because they allow for easy adjustment of the amount of Si-H groups in one molecule while exhibiting peelability. The terminal silicon atoms may have Si-H groups, but it is preferable that they have a trialkylsilane structure such as trimethylsilane.

Examples of Si-H group-containing silicones include organohydrogenpolysiloxanes represented by the following general formula (II).

(In general formula (II), ^R3 is a monovalent hydrocarbon group having 1 to 16 carbon atoms, which may be the same or different alkyl or aryl group, and when a2 + b2 is 100 mol%, a2 is 30 mol% to 90 mol%, and b2 is 10 mol% to 70 mol%.)

[SiO] The silicon atom represented by _a2 is bonded to a hydrogen atom (hydrogen group), and ^R3 may be a monovalent hydrocarbon group containing an alkyl group or an aryl group, but it is preferable that it be a monovalent hydrocarbon group with 1 to 16 carbon atoms selected from alkyl groups or aryl groups.

[SiO] _b2 and ^R3 bonded to the terminal Si atom may be monovalent hydrocarbon groups containing an alkyl group or an aryl group, but it is preferable that they be monovalent hydrocarbon groups with 1 to 16 carbon atoms selected from alkyl groups or aryl groups.

For all ^{R3 groups} , a smaller number of carbon atoms in the alkyl or aryl group is preferable, as this reduces steric hindrance and facilitates the crosslinking reaction. It is also preferable from the viewpoint of fluidity and uniformity of the reaction structure in the release layer. For this reason, preferred alkyl groups include methyl, ethyl, propyl, and butyl groups, while preferred aryl groups include phenyl and tolyl groups.

When the total constituent units of [SiO] _a2 and [SiO] _b2 are assumed to be 100 mol%, the range of constituent units of [SiO] _a2 is preferably 30 mol% to 90 mol%, and more preferably 40 mol% to 80 mol%. When the constituent units of [SiO] _a2 are 30 mol% or more, there is a sufficient amount of crosslinking reaction sites, the cohesive force of the release layer increases, and the abrasion resistance and solvent resistance of the release layer are also good, which is preferable. Furthermore, when the constituent units of [SiO] _a2 are 90 mol% or less, Si-H groups are less likely to remain in the release layer, the activity of the release layer surface does not increase easily, and good release properties are maintained, which is preferable.

In this invention, the number-average molecular weight of the Si-H group-containing silicone is preferably 1000 to 5000, and more preferably 3000 to 5000. A number-average molecular weight of 1000 or more makes it easier to obtain sufficient release properties. On the other hand, a number-average molecular weight of 5000 or less tends to result in good emulsification properties in aqueous coating compositions and good coating uniformity. Furthermore, the crosslinking reaction proceeds more efficiently, reducing the amount of residual Si-H groups in the release layer and improving release properties.

In the aqueous coating composition, it is preferable that the composition contains 1 to 50 parts by mass of Si-H group-containing silicone per 100 parts by mass of alkenyl group-containing silicone, more preferably 2 to 40 parts by mass, and even more preferably 3 to 30 parts by mass. A Si-H group-containing silicone content of 1 part by mass or more is preferable because it provides a sufficient number of crosslinking reaction sites, facilitates the formation of a dense crosslinked structure, and improves release properties. A Si-H group-containing silicone content of 50 parts by mass or less is preferable because it reduces the likelihood of Si-H groups remaining in the release layer, preventing increased surface activity of the release layer and maintaining good peelability.

(Platinum-based catalyst)
The crosslinking reaction between alkenyl group-containing silicone and Si-H group-containing silicone is an addition reaction, and in one embodiment, it is preferable to use a platinum-based catalyst to promote the reaction.

Known platinum-based catalysts can be used, such as platinum chloride and chloroplatinic acid. Considering dispersibility in silicone, a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt catalyst) may also be used. By dispersing it simultaneously with the emulsification of the silicone, uniform dispersion can be ensured.

The platinum-based catalyst content is preferably in the range of 10 ppm to 400 ppm relative to the combined mass of the alkenyl group-containing silicone and the Si-H group-containing silicone. This range allows for sufficient curing of the silicone, suppresses the formation of silicone aggregates, and yields a release film with excellent surface properties. When the mass ratio of platinum is below the upper limit, the addition reaction between the alkenyl groups and Si-H groups becomes moderate, tending to suppress the formation of silicone aggregates. From this viewpoint, the platinum-based catalyst content is more preferably 300 ppm or less, and even more preferably 200 ppm or less. Furthermore, when the mass ratio of platinum is above the lower limit, the addition reaction proceeds sufficiently, making it less likely to cause poor silicone curing. From this viewpoint, the platinum catalyst content is more preferably 15 ppm or more, and even more preferably 20 ppm or more.

(Aqueous solvent)
Aqueous coating compositions typically contain an alkenyl group-containing silicone and a Si-H group-containing silicone, as well as an aqueous solvent, with water being preferred as the aqueous solvent. In one embodiment, an aqueous dispersion of alkenyl group-containing silicone and an aqueous dispersion of Si-H group-containing silicone are used for the preparation of an aqueous coating composition. An aqueous emulsion is preferably used as the aqueous dispersion of each silicone.

The release layer is formed from such an aqueous emulsion, and the release layer is formed by applying an aqueous coating composition containing the aqueous emulsion (hereinafter sometimes abbreviated as "aqueous coating solution"). By using an aqueous solvent, the release layer can be formed without the need for explosion-proof and recovery equipment required for organic solvents during the film manufacturing process. A small amount of organic solvent may be included if necessary.

(Other ingredients)
In one embodiment, other additives such as surfactants, coupling agents, crosslinking reaction inhibitors, antistatic agents, ultraviolet absorbers, pigments, colorants, organic or inorganic particles, lubricants, and antiblocking agents can be mixed into the aqueous coating composition, provided that the effects of the invention are not impaired.

(Surfactants)
In one embodiment, it is preferable to add a surfactant to the aqueous coating composition in order to promote wetting of the substrate film when forming the release layer. Examples of such surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants, and it is possible to use one or more of these. In order to prevent aggregation of the aqueous emulsions of each silicone and not to affect the curing reaction of the silicone, it is preferable to use a nonionic surfactant as an emulsifier.

Nonionic surfactants are preferably those with an HLB value in the range of 6 to 18. Examples include at least one selected from alkylene oxide adducts of higher alcohols or higher fatty acids, esters of alkylene oxide adducts of higher fatty acids and alcohols, alkylene oxide adducts of alkanolamides, alkylene oxide adducts of sorbitan esters, and alkylene oxide adducts of higher fatty acid glycerides. Here, the HLB value is calculated using Griffin's formula.

Examples of alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide. One or more of these may be used. When multiple are used, the addition method (block or random) is acceptable, but the HLB value is preferably in the range of 8 to 18, and more preferably in the range of 10 to 15. Among these nonionic surfactants, polyoxyethylene lauryl ether and polyoxyethylene tridecyl ether are preferred. Two or more nonionic surfactants may be mixed as needed. Using a nonionic surfactant with an HLB value outside the specified range as an emulsifier for a silicone aqueous dispersion may reduce the emulsifying and dispersing power and the stability of the aqueous dispersion.

The surfactant is preferably used in an amount of 0.1% to 20% by mass relative to the total solids, more preferably in an amount of 0.2% to 15% by mass, and even more preferably in an amount of 0.5% to 10% by mass. Above the lower limit of this range, the emulsification state is good, while below the upper limit, excessive peeling is less likely to occur.

(Crosslinking reaction inhibitor)
In one embodiment, it is preferable that a reaction inhibitor is included in the aqueous coating solution to suppress the activity of the platinum-based catalyst at room temperature. Such a reaction inhibitor is preferably a reaction inhibitor having an alkynyl group. The reaction inhibitor having an alkynyl group is not particularly limited as long as it has an alkynyl group, but specific examples include 1-ethynyl-1-cyclohexanol, 4-ethyl-1-octin-3-ol, 3-methyl-1-dodecine-3-ol, 3,7,11-trimethyl-1-dodecine-3-ol, 1,1-diphenyl-2-propyne-3-ol, 3-ethyl-6-ethyl-1-nonine-3-ol, 3-methyl-1-pentadecin-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 3-phenyl-1-butyne-3-ol. In this invention, since the coating solution is aqueous, it is preferable to use a reaction inhibitor having an alkynyl group and a hydroxyl group, as exemplified, considering the balance between affinity and solubility in water, coordination ability to platinum, and boiling point. Alternatively, the platinum-based catalyst may be mixed with a common organopolysiloxane and used as an aqueous emulsion for addition to the aqueous coating solution.

The crosslinking reaction inhibitor content is preferably 5 ppm to 1000 ppm, more preferably 10 ppm to 700 ppm, and even more preferably 20 ppm to 500 ppm, relative to the mass of the aqueous coating composition used to form the release layer. When the crosslinking reaction inhibitor content is above the lower limit, the pot life is extended, the addition curing reaction of the silicone at room temperature is less likely to proceed, and silicone aggregates tend to be less likely to form. Furthermore, when the crosslinking reaction inhibitor content is below the upper limit, the silicone is less likely to migrate to the mating material after peeling, and the amount of reaction inhibitor volatilized during heat treatment is reduced, thus minimizing contamination inside the oven.

(Coupling agent)
In one embodiment, a coupling agent may be added to the aqueous coating composition to improve the adhesion between the silicone component and the substrate film. The coupling agent may be a compound represented by the general formula _YRSiX3 , for example, a silane coupling agent. Here, Y is an organic functional group such as a vinyl group, epoxy group, amino group, or mercapto group, and it is particularly preferable that Y is an epoxy group or a vinyl group.

R is an alkylene group such as a methylene, ethylene, or propylene group, or a single bond. X is a hydrolyzable group such as a methoxy group, ethoxy group, or acetoxy group, or an alkyl group, where at least one of the three X groups is hydrolyzable, preferably all three X groups. A methoxy group is preferred as the hydrolyzable group.

Preferred silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, and vinylmethyldimethoxysilane.

Other examples of coupling agents include organometallic compounds containing metals such as zirconium, titanium, and aluminum. Organometallic compounds classified as alkoxides, chelates, or acylates are preferred. Specific examples include, but are not limited to, zirconium tetraacetylacetonate, zirconium acetate, titanium acetylacetonate, triethanolamine titanate, and titanium lactate.

Furthermore, it is possible to use two or more coupling agents, such as using a silane coupling agent where Y is an epoxy group and a silane coupling agent where Y is a vinyl group in combination.

In one embodiment, the addition of a coupling agent improves the durable adhesion between the silicone, the main component of the release layer, and the polyester film, etc. For example, during solution casting of resin sheets using organic solvents, organic solvent components may penetrate the release layer, potentially causing erosion. However, the addition of a coupling agent can suppress this erosion. During melt casting of resin sheets at high temperatures, the release layer is exposed to high temperatures, potentially leading to thermal degradation. However, the addition of a coupling agent can suppress thermal degradation and maintain the release layer.

From the above perspective, the coupling agent content is preferably 0.1 parts by mass or more and 20 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass or less, based on 100 parts by mass of the total amount of alkenyl group-containing silicone and Si-H group-containing silicone contained in the release layer.

(Preparation of silicone aqueous dispersion)
In one embodiment, the preparation of an aqueous emulsion involves emulsifying a predetermined alkenyl group-containing silicone or Si-H group-containing silicone, an aqueous solvent, and a surfactant. Known methods can be used to emulsify these components; for example, a method can be used in which a predetermined silicone, surfactant, and other components prepared in advance are mechanically emulsified in an aqueous medium using a stirring device such as a homogenizer, an adio-homo mixer, or an ultraplanetary mixer.

Furthermore, the particle size of the aqueous dispersion can be adjusted by controlling the size of the stirring blade, the stirring speed, and the stirring time. The average particle size of the dispersed particles in each silicone aqueous dispersion is preferably 200 nm or less, and more preferably 100 nm to 200 nm.

[Base film]
The base film in the present invention is not particularly limited, but examples include sheets or films made of polyester such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polycarbonate, polyethylene, and polypropylene, polystyrene triacetylcellulose, acrylic, and polyimide. Among these, films made of polyester are preferred from the viewpoint of having excellent mechanical properties and heat resistance, and a good balance between these properties and price. The following explanation will use the case of a polyester film as an example, but even when other resin films are used, the copolymer components, blending components, additives, film manufacturing method, laminated structure, etc., are the same as described below.

(Polyester film)
The polyester used as the base film is not particularly limited, and a film-formed polyester commonly used as a base film for release films can be used. Preferably, it is a crystalline linear saturated polyester composed of an aromatic dibasic acid component and a diol component, and more preferably, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or copolymers mainly composed of these resin components. In particular, a polyester film formed from polyethylene terephthalate is especially preferred. The polyethylene terephthalate preferably has 90 mol% or more, more preferably 95 mol% or more of repeating units of ethylene terephthalate, and may also have small amounts of other dicarboxylic acid components and diol components copolymerized. For example, from the viewpoint of cost, it is preferable to have one produced only from terephthalic acid and ethylene glycol. In addition, known additives, such as antioxidants, light stabilizers, ultraviolet absorbers, and crystallizers, may be added within a range that does not hinder the effect of the release film of the present invention. The polyester film is preferably a biaxially oriented polyester film due to reasons such as high bidirectional elastic modulus.

The intrinsic viscosity of the above polyester film is preferably 0.50 dl/g or more and 0.70 dl/g or less, and more preferably 0.52 dl/g or more and 0.62 dl/g or less. An intrinsic viscosity of 0.50 dl/g or higher is preferable because it prevents frequent breakage during the stretching process. Conversely, an intrinsic viscosity of 0.70 dl/g or less is preferable because it provides good cutability when cutting to a predetermined product width and prevents dimensional defects. Furthermore, it is preferable to thoroughly vacuum-dry the raw material pellets.

In this specification, when "polyester film" is simply referred to, it means a polyester film having surface layer A and surface layer B (a laminated polyester film).

The method for manufacturing the polyester film in this invention is not particularly limited, and conventionally used methods can be employed. For example, the polyester can be melted in an extruder, extruded into a film, and cooled in a rotating cooling drum to obtain an unstretched film. This unstretched film can then be biaxially stretched to obtain the film. The biaxially oriented film can be obtained by sequentially biaxially stretching a uniaxially oriented film in the longitudinal or transverse direction in the transverse or longitudinal direction, or by simultaneously biaxially stretching an unstretched film in both the longitudinal and transverse directions.

In this invention, it is preferable that the stretching temperature during polyester film stretching be above the secondary transition temperature (Tg) of polyester. It is particularly preferable to stretch the film by 1x to 8x, and especially by 2x to 6x, in both the longitudinal and transverse directions.

The polyester film described above preferably has a thickness of 12 μm to 50 μm, more preferably 15 μm to 38 μm, and more preferably 19 μm to 33 μm. A film thickness of 12 μm or more is preferable because it avoids deformation due to heat during film production, processing, and molding. On the other hand, a film thickness of 50 μm or less is preferable because it avoids excessively large amounts of film waste after use, thus reducing the environmental impact.

The above-mentioned polyester film substrate may be a single layer or a multilayer of two or more layers. For example, the substrate film may be a polyester film having a surface layer A that substantially does not contain particles with a particle size of 1.0 μm or larger, and a surface layer B that contains particles. Preferably, surface layer A substantially does not contain inorganic particles with a particle size of 1.0 μm or larger.

In this embodiment, the surface layer A may contain particles with a particle size of less than 1.0 μm and 1 nm or larger. By substantially excluding particles with a particle size of 1.0 μm or larger, such as inorganic particles, from the surface layer A, the transfer of particle shape from the substrate to the resin sheet, which can cause defects, can be reduced.

In one embodiment, by not including any particles with a particle size of less than 1.0 μm in the surface layer A, it is possible to more effectively suppress defects caused by the transfer of the particle shape in the substrate to the resin sheet.
In one embodiment, the polyester film substrate is preferably a laminated film having a surface layer A on at least one side that is substantially free of inorganic particles. This makes it possible to more effectively suppress defects caused by the transfer of the particle shape in the substrate to the resin sheet.
For example, a surface layer A that substantially does not contain particles with a particle size of less than 1.0 μm is preferably also substantially free of particles with a particle size of 1.0 μm or larger.

In this invention, "substantially free of particles" means, for example, in the case of inorganic particles smaller than 1.0 μm, that the content of inorganic elements when quantified by fluorescence X-ray analysis 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 film, contaminants originating from foreign substances, or dirt adhering to the raw material resin or the production lines and equipment in the film manufacturing process, can detach and become mixed into the film. Furthermore, "substantially free of particles with a particle size of 1.0 μm or larger" means that particles with a particle size of 1.0 μm or larger are actively not included.

In the case of a laminated polyester film consisting of two or more multilayer structures, it is preferable that the surface opposite to surface layer A, which substantially does not contain inorganic particles, has a surface layer B that may contain inorganic particles.

In terms of the lamination structure, if the layer on the side where the release layer is applied is designated as layer A, the layer on the opposite side as layer B, and the remaining core layer as layer C, then the layer configuration in the thickness direction can be a laminated structure such as release layer/A/B or release layer/A/C/B. Naturally, layer C may consist of multiple layers. Furthermore, the surface layer B may not contain inorganic particles. In that case, to provide slipperiness for winding the film into a roll, it is preferable to provide a coating layer containing at least inorganic particles and a binder on the surface layer B.

In the polyester film substrate of the present invention, the surface layer B, which forms the surface opposite to the surface to which the release layer is applied, preferably contains inorganic particles from the viewpoint of the film's slipperiness and ease of air release, and particularly preferably uses silica particles and/or calcium carbonate particles. The inorganic particle content is preferably 5,000 ppm to 15,000 ppm in total within the surface layer B.

In this case, the average surface roughness (Sa) of the surface layer B film is preferably in the range of 1 nm to 40 nm. More preferably, it is in the range of 5 nm to 35 nm. When the total amount of silica particles and/or calcium carbonate particles is 5000 ppm or more and Sa is 1 nm or more, air can be uniformly released when the film is wound into a roll, resulting in a good winding shape and good flatness, making it suitable for the manufacture of ultrathin ceramic green sheets. Furthermore, when the total amount of silica particles and/or calcium carbonate particles is 15000 ppm or less and Sa is 40 nm or less, lubricant aggregation is less likely to occur, and no coarse protrusions are formed, resulting in stable quality during the manufacture of ultrathin ceramic green sheets, which is preferable.

As particles contained in the above-mentioned B layer, inert inorganic particles and/or heat-resistant organic particles other than silica and/or calcium carbonate can also be used, but from the viewpoint of transparency and cost, silica particles and/or calcium carbonate particles are more preferable. Other inorganic particles that can be used include alumina-silica composite oxide particles and hydroxyapatite particles. Heat-resistant organic particles include cross-linked polyacrylic particles, cross-linked polystyrene particles, and benzoguanamine particles. When silica particles are used, porous colloidal silica is preferred, and when calcium carbonate particles are used, light calcium carbonate surface-treated with a polyacrylic acid-based polymer compound is preferred from the viewpoint of preventing lubricant detachment.

The average particle size of the inorganic particles added to the surface layer B is preferably 0.1 μm or more and 2.0 μm or less, and particularly preferably 0.5 μm or more and 1.0 μm or less. An average particle size of 0.1 μm or more is preferable because it provides good slipperiness to the release film. Furthermore, an average particle size of 2.0 μm or less is preferable because it does not adversely affect the smoothness of the release layer surface, thus preventing the formation of pinholes in the ceramic green sheet.

From the viewpoint of reducing pinholes, it is preferable not to use recycled materials or similar materials in the surface layer A, which is the layer on the side where the release layer is provided, in order to prevent the inclusion of inorganic particles such as lubricants.

The thickness ratio of surface layer A, which is the layer on the side where the release layer is provided, is preferably 20% to 50% of the total thickness of the base film. A ratio of 20% or more is preferable because it reduces the influence of particles contained in surface layer B and other layers from within the film, making it easier for the average surface roughness Sa to satisfy the above range. A ratio of 50% or less of the total thickness of the base film allows for an increase in the proportion of recycled materials used in surface layer B, resulting in a lower environmental impact, which is preferable.

Furthermore, from an economic standpoint, layers other than the surface layer A (surface layer B or the aforementioned intermediate layer C) can use 50% to 90% by mass of recycled film scraps or PET bottles. Even in this case, it is preferable that the type, amount, particle size, and average surface roughness (Sa) of the lubricant contained in layer B satisfy the above range.

Furthermore, to improve the adhesion of subsequent release layers and prevent static electricity, a coating layer may be applied to the surface of surface layer A and/or surface layer B before stretching or after uniaxial stretching during the film-forming process. Surface treatments may also be applied.

In one embodiment, the surface to which the aqueous coating composition is applied to form the release layer can be surface-treated or an easy-adhesion layer can be provided to enhance adhesion to the release layer. Examples of surface treatments include plasma treatment, corona discharge treatment, ultraviolet treatment, flame treatment, and electron beam/radiation treatment. Examples of easy-adhesion layers include layers containing the same resin as the base film, and further containing antistatic agents, pigments, surfactants, lubricants, antiblocking agents, etc. If an adhesion-enhancing agent such as a coupling agent is added to the aqueous coating composition, the release layer can have sufficient adhesion to the base film even without providing an easy-adhesion layer.

[Formation of release layer]
In one embodiment, the release layer is formed by applying an aqueous coating composition containing an aqueous emulsion of alkenyl group-containing silicone and an aqueous emulsion of Si-H group-containing silicone. In this case, the release layer is formed on at least one surface of the base film. The release layer is formed by applying the aqueous coating solution onto the base film, followed by heating and drying, during which the components of the aqueous coating solution react and solidify. It is preferable that the release layer is formed during the film manufacturing process.

The thickness of the release layer after drying is preferably 5 nm to 100 nm. If the thickness of the release layer is above the lower limit, sufficient release properties are easily obtained. If it is below the upper limit, the release strength tends not to increase easily. Furthermore, it eliminates the need to increase the concentration of the release layer component in the water-based coating solution or increase the coating amount, making application easier. Therefore, the thickness of the release layer is more preferably 5 nm to 70 nm, and even more preferably 5 nm to 50 nm.

When applying the aqueous coating solution onto a substrate film, the solid content concentration is preferably 20% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, based on the release layer component in the aqueous coating solution. When the solid content concentration of the release layer component in the aqueous coating solution is above the lower limit, film-forming properties tend to improve. Furthermore, when the solid content concentration is below the upper limit, the stability of the aqueous coating solution and the appearance of the release layer tend to improve. Water is preferably used as the aqueous solvent for adjusting the solid content concentration.

The aqueous coating solution applied to the base film to form a release layer can be carried out at any stage, but it is preferable to do so during the polyester film manufacturing process, and more preferably, to apply it to the polyester film before orientation crystallization is complete. Afterward, the film can be stretched in at least one direction, followed by heat treatment to complete the crystal orientation.

Here, polyester films before crystal orientation is complete include unstretched films, uniaxially oriented films in which the unstretched film is oriented in either the longitudinal direction (hereinafter sometimes referred to as the continuous film formation direction, longitudinal direction, or MD direction) or the transverse direction (hereinafter sometimes referred to as the direction perpendicular to the longitudinal direction, width direction, or TD direction), and films that have been low-magnification stretched and oriented in both the longitudinal and transverse directions (biaxially oriented films before final re-stretching in the longitudinal or transverse direction to complete orientation crystallization).

In particular, so-called in-line coating is preferred, in which an aqueous coating solution is applied to an unstretched film or a uniaxially oriented film, and then longitudinal and/or transverse stretching and heat fixing are performed immediately. The release layer may be dried by the stretching or heat fixing process after coating, and a further drying process may be added as needed. Furthermore, when curing the composition using a catalyst to obtain a cured film, curing can be achieved by the stretching or heat fixing process, and a further curing process may be added as needed.

When applying an aqueous coating solution to a polyester film, it is preferable to perform a preliminary physical treatment on the film surface, such as corona surface treatment, flame treatment, or plasma treatment, to improve coating properties, or to use the aforementioned emulsifier as a wetting agent in combination with the composition, or to add a surfactant as a wetting agent.

Any known coating method can be applied. For example, roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, and curtain coating methods can be used individually or in combination.

[Characteristics of release film]
In the present invention, the surface free energy of the release layer in the test method described later is preferably in the range of 10 mN/m to 40 mN/m, more preferably 12 mN/m to 38 mN/m, even more preferably 14 mN/m to 36 mN/m, and particularly preferably 15 mN/m to 35 mN/m. If the surface free energy of the release layer is below the upper limit, the adhesion force is reduced and severe peeling becomes less likely. If it is above the lower limit, defects due to repulsion of the processed layer such as a ceramic sheet or resin sheet coated on the surface of the release layer are less likely to occur, and pinhole defects are also less likely to occur.

[Application]
The release film in this invention can be used as a process film during the manufacture of multilayer ceramic capacitors or resin sheet casting. In particular, even when a thin resin sheet with a thickness of 1 μm or less after drying is produced, the wettability is good, so pinholes in the processed layer are reduced, and for example, when used as a release film for the manufacture of green sheets, the defect rate of thin-walled multilayer ceramic capacitors can be reduced.

The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The evaluation methods for physical properties, etc., in the following examples are as follows.

(1) Uniformity of the release layer coating The release film was cut into A4 size sheets, and the release layer surface was visually observed using a fluorescent lamp and a halogen light. The number of aggregated coating defects (number per A4 sheet) was compared and evaluated according to the following criteria.
◎: No coating defects ○: 1-2 coating defects △: 3-5 coating defects ×: 6 or more coating defects

(2) Surface Free Energy of the Release Layer For samples that had been conditioned for 24 hours under conditions of 23°C and 50% RH, the static contact angle was measured using a contact angle meter (DMo-501, manufactured by Kyowa Interface Chemical Co., Ltd.) after water was dropped onto the samples and allowed to stand for 30 seconds. Similarly, the static contact angles of ethylene glycol and methylene iodide were measured, and the following simultaneous equations relating to the surface tension components of the release layer were constructed using the surface tension components of each liquid listed below (the measured solutions for water, ethylene glycol, and methylene iodide are designated as 1, 2, and 3 respectively; γLD is the dispersion force component of the liquid, γLP is the polar force component of the liquid, γLH is the hydrogen bonding component of the liquid, γL is the sum of the surface tension components in the liquid, γSD is the dispersion force component of the release layer, γSP is the polar force component of the release layer, and γSH is the hydrogen bonding component of the release layer. θ represents the contact angle).
(γSD・γLD1) ^1/2 + (γSP・γLP1) ^1/2 + (γSH・γLH1) ^1/2 = γL1 (1+cosθ1)/2
(γSD・γLD2) ^1/2 + (γSP・γLP2) ^1/2 + (γSH・γLH2) ^1/2 = γL2 (1+cosθ2)/2
(γSD・γLD3) ^1/2 + (γSP・γLP3) ^1/2 + (γSH・γLH3) ^1/2 = γL3 (1+cosθ3)/2
The γLD, γLP, γLH, and γL values for water, ethylene glycol, and methylene iodide are shown in Table 1.

Next, the surface free energy γS of the release layer surface was calculated using the following formula based on the values of γSD, γSP, and γSH obtained above.
γS=γSD+γSP+γSH

(3) Smear test of the release layer (abrasion resistance)
The release surface of the release film was rubbed once with an index finger under a load of approximately 500 gf, and the whitening state of the surface of the release layer was visually observed and evaluated according to the following criteria.
○: No change △: Slight whitening ×: Whitening

(4) Release layer rub-off test (adhesion)
The release surface of the release film was rubbed 10 times with a thumb under a load of approximately 500 gf. To check for silicone detachment in that area, adhesive tape (manufactured by Nitto Denko Corporation, product name "31B Tape") was applied, and the peeling state of the adhesive tape was checked and evaluated according to the following criteria.
○: No change in peeling when the adhesive tape is removed. △: Slight change in peeling when the adhesive tape is removed. ×: Change in peeling when the adhesive tape is removed.

(5) Ceramic Sheet Release Properties 100 parts by mass of barium titanate ( _BaTiO3 , manufactured by Kyoritsu Material Co., Ltd.), 7 parts by mass of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd.), 3 parts by mass of dioctyl phthalate, and 3 parts by mass of dispersant (DISPERBY K-103, manufactured by BIC Chemie Co., Ltd.) were added to a mixed solvent of toluene:ethanol = 1:1 (volume ratio) and dispersed in a ball mill to prepare a slurry. This slurry was uniformly coated onto the release layer of a release film so that the thickness after drying would be 2 μm, and then dried to form a ceramic sheet. The release film on which the ceramic sheet was formed was cut to 25 mm x 150 mm, and adhesive tape (manufactured by Nitto Denko Corporation, product name "31B Tape") was attached to the ceramic sheet side to prepare a test piece. The test specimen was conditioned for 24 hours at 23°C and 50% humidity. Then, the ceramic sheet was peeled using a tensile testing machine at a peel angle of 180° and a peel speed of 300 mm/min, and the peel strength was measured. The peel strength of the ceramic sheet was evaluated based on the following indicators.
◎: Peel strength is less than 1 g/25 mm. ○: Peel strength is 1 g/25 mm or more, and less than 3 g/25 mm. △: Peel strength is 3 g/25 mm or more, and 12 g/25 mm or less. ×: Peel strength exceeds 12 g/25 mm, or the ceramic sheet tears.

(6) Recyclability Evaluation Recyclability was assessed by using a universal projector to magnify the size and number of foreign objects contained in the film by 20 times using projectile irradiation, and counting the number of foreign objects with a maximum diameter of 50 μm or more. The measurement area was set to 0.05 ^m² .
◎: Number of foreign objects: less than 10 per 0.05 ^m² ; no problem for use.
○: If the number of foreign objects is 10 or more per 0.05 ^m² but less than 30 per 0.05 ^m² , it slightly affects flatness, but does not pose a problem for use.
△: If the number of foreign objects is 30 or more per 0.05 ^m² but less than 100 per 0.05 ^m² , it can be used with limited applications.
×: If the number of foreign objects is 100 or more per 0.05 ^m² , the deformation of the cast surface is significant and noticeable, making it unusable.

(7) Number-average molecular weight: Gel permeation chromatography (GPC) was measured and calculated as a polystyrene equivalent.

(8) Thickness of the release layer After cutting the release film into small triangular pieces, a 2 nm thick Pt (platinum) layer was formed on the surface of the release layer by coating. The obtained samples were fixed in a multiaxial embedding capsule and embedded using epoxy resin. Using a microtome ULTRACUT-S, the film was sliced perpendicular to the plane direction to obtain ultrathin samples with a thickness of 50 nm. Next, the obtained ultrathin samples were placed on a grid and vapor-stained with 2% osmium acid at 60°C for 2 hours. Using the ultrathin samples after vapor staining, the film cross-section was observed with a transmission electron microscope LEM-2000 at an acceleration voltage of 100 kV to measure the thickness of the release layer. Measurements were performed at 10 arbitrary points, and the average value was taken as the thickness of the release layer (unit: nm).

[Example 1]
Polyethylene terephthalate ([η] = 0.65 dl/g, Tg = 78°C) containing 0.15% by mass of calcium carbonate particles with an average particle size of 0.6 μm was melted in an extruder, passed through a filter with a filtration accuracy of 10 μm, extruded from a die, and cooled in a cooling drum by conventional methods to obtain an unstretched film. Next, it was stretched 3.2 times in the longitudinal direction at 80°C, and then the aqueous coating solution (aqueous coating composition) obtained in Production Example 1 was uniformly applied using a roll coater so that the release layer thickness was as shown in Table 2 for the product thickness. The aqueous coating solution used was prepared within 24 hours.

Next, the coated film was dried at 105°C, stretched 4.6 times its original size in the transverse direction at 145°C, and then heat-set at 230°C for approximately 10 seconds to obtain a release film (thickness 25 μm) having a release layer formed by the reaction and solidification of the aqueous coating solution. This film was then evaluated. The evaluation results are shown in Table 2.

Furthermore, for each example and comparative example, the release film portions that did not become part of the final product during the product roll collection process, as well as release film with defects that prevented it from becoming part of the final product, were crushed until the film piece diameter was approximately 5 mm or less, melted, and recycled into 45% by mass of the recycled raw material.

<Manufacturing Example 1>
(Sample 1A)
Using an emulsifying device capable of stirring the entire contents of a container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), a raw material consisting of 95% by mass of silicone oil represented by formula (A) 2 mol%, formula (B) 4 mol%, formula (C) 90 mol%, formula (D) 2 mol%, and formula (E) 2 mol%, with a number average molecular weight of 8000, and 5% by mass of polyoxyethylene tridecyl ether (manufactured by ADEKA Corporation, product name "ADEKATOL TN-100") as a surfactant was mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of Sample 1A with a solid content of 45% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification.

(Sample 2A)
Using an emulsifying device capable of stirring the entire contents of a container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), a raw material consisting of 95% by mass of silicone oil in formula (F) where a3 is 60 mol%, b3 is 40 mol%, and the number average molecular weight is 4000, and 5% by mass of polyoxyethylene tridecyl ether (manufactured by ADEKA Corporation, product name "ADEKATOL TN-100") as a surfactant was mechanically emulsified in an aqueous medium to obtain an aqueous dispersion of Sample 2 with a solid content of 40% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

(Water-based coating solution)
As an aqueous coating solution, Sample 1A and Sample 2A were prepared so that the solid content mass of the silicone was as shown in Table 2, and the other components were as follows. 5% by mass of the coupling agent listed below relative to the total mass of silicone, 50 ppm of the platinum-based catalyst listed below relative to the total solid content mass of Sample 1 and Sample 2, and 100 ppm of the crosslinking reaction inhibitor listed below relative to the mass of the aqueous coating solution were mixed. The aqueous coating solution was then diluted with water to achieve the target release layer thickness.
• Coupling agent: 3-Glycidoxypropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBE-403")
• Platinum-based catalyst: Platinum-based catalyst emulsion (manufactured by Wacker, product name "CATALYST EM440")
• Crosslinking reaction inhibitor: 1-ethinylcyclohexanol (manufactured by Alfa Lancaster)

[Examples 2-3]
In Example 1, the release film was prepared under exactly the same conditions as in Example 1, except that the contents of Sample 1A and Sample 2A were changed when preparing the aqueous coating solution, as shown in Table 2. The evaluation described above was then performed. The results are shown in Table 2.

[Example 4]
In Example 2, the release film was prepared under exactly the same conditions as in Example 2, except that the aqueous coating solution was prepared using Sample 1B, which was produced in Production Example 2, instead of Sample 1A. The evaluation described above was then performed. The results are shown in Table 2.

<Manufacturing Example 2> (Sample 1B)
Using an emulsifying device capable of stirring the entire contents of a container (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer"), a raw material consisting of 95% by mass of silicone oil represented by formula (A) 3 mol%, formula (B) 7 mol%, formula (C) 85 mol%, formula (D) 2 mol%, and formula (E) 3 mol%, with a number average molecular weight of 4000, and 5% by mass of polyoxyethylene tridecyl ether (manufactured by ADEKA Corporation, product name "ADEKATOL TN-100") as a surfactant was mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of Sample 1B with a solid content of 50% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 180 nm by adjusting the stirring speed and stirring time during emulsification.

[Example 5]
In Example 2, the release film was prepared under exactly the same conditions as in Example 2, except that the aqueous coating solution was prepared using Sample 1C, which was produced in Production Example 3, instead of Sample 1A. The evaluation described above was then performed. The results are shown in Table 2.

<Manufacturing Example 3> (Sample 1C)
Using an emulsifying device capable of stirring the entire contents of a container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), a raw material consisting of 95% by mass of silicone oil represented by formula (A) at 10 mol%, formula (B) at 5 mol%, formula (C) at 84 mol%, formula (D) at 1 mol%, and formula (E) at 10 mol%, with a number average molecular weight of 6000, and 5% by mass of polyoxyethylene tridecyl ether (manufactured by ADEKA Corporation, product name "ADEKATOL TN-100") as a surfactant was mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of Sample 1C with a solid content of 40% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 210 nm by adjusting the stirring speed and stirring time during emulsification.

[Comparative Examples 1-3]
In Examples 1 to 3, release films were prepared under exactly the same conditions as in Examples 1 to 3, except that the aqueous coating solution obtained in Production Example 4 was used instead of the aqueous coating solution obtained in Production Example 1, and the aforementioned evaluation was performed. The results are shown in Table 2.

<Manufacturing Example 4>
(Sample 1D)
Using an emulsifying device capable of stirring the entire contents of a container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), a raw material consisting of 95% by mass of silicone oil represented by formula (A) at 30 mol%, formula (B) at 5 mol%, formula (C) at 30 mol%, formula (D) at 1 mol%, and formula (E) at 34 mol%, with a number average molecular weight of 250,000, and 5% by mass of polyoxyethylene tridecyl ether (manufactured by ADEKA Corporation, product name "ADEKATOL TN-100") as a surfactant was mechanically emulsified in an aqueous medium to obtain an aqueous emulsion of sample 1D with a solid content of 40% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 300 nm by adjusting the stirring speed and stirring time during emulsification.

(Sample 2B)
Using an emulsifying device capable of stirring the entire contents of a container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), a raw material consisting of 95% by mass of silicone oil in which a3 of formula (F) is 50 mol%, b3 is 50 mol%, and the number average molecular weight is 8000, and 5% by mass of polyoxyethylene tridecyl ether (manufactured by ADEKA Corporation, product name "Adekatol TN-100") as a surfactant was mechanically emulsified in an aqueous medium to obtain an aqueous dispersion of Sample 2 with a solid content of 50% by mass. Furthermore, the emulsion particle size was adjusted to an average particle size of 210 nm by adjusting the stirring speed and stirring time during emulsification.

(Water-based coating solution)
The aqueous coating solution was prepared under the same conditions as in Production Example 1, except that the solid content mass of the silicone in Sample 1D and Sample 2B was adjusted to the amounts shown in Table 2.

[Comparative Example 4]
A substrate film was prepared in the same manner as in Example 1, except that a release layer was not applied. A mixture was prepared containing 80% by mass of silicone: SD-7335 (manufactured by Dow-Toray Industries, Ltd., addition reaction type, number average molecular weight 900,000), 20% by mass of silicone: SD-7236 (manufactured by Dow-Toray Industries, Ltd., addition reaction type containing silicone resin, number average molecular weight 580,000), and 0.02% by mass of catalyst: SRX-212 (manufactured by Dow-Toray Industries, Ltd.). The solid content of the coating solution was diluted with toluene to achieve the target release layer thickness, and the coating solution was prepared. The coating solution was applied to the substrate film using a coating machine to form a release layer, and drying was carried out at a temperature of 150°C for 30 seconds to produce a release film, which was then evaluated as described above. The results are shown in Table 2. Furthermore, because an organic solvent is used to form the release layer, special explosion-proof equipment is required, and exhaust treatment of the dried organic solvent is also required in addition to that in the example.
[Comparative Example 5]
A substrate film was prepared in the same manner as in Example 1, except that a release layer was not applied. A mixture was prepared containing 88% by mass of silicone with a solid content ratio of 96 mol% a1 and 4 mol% b1 in formula (1), and a number average molecular weight of 150,000; 9% by mass of silicone with a solid content ratio of 80 mol% a2 and 20 mol% b2 in formula (2), and a number average molecular weight of 20,000; and 3% by mass of catalyst: CM670 (Momentive). The required amount of platinum-based catalyst was added, and the solid content concentration of the coating solution was diluted with an organic solvent of 70% by mass/30% by mass of methyl ethyl ketone and toluene to achieve the target release layer thickness. The coating solution was applied to the substrate film using a coating machine to form a release layer, and drying was carried out at a temperature of 130°C for 30 seconds to produce a release film, which was then evaluated as described above. The results are shown in Table 2. Furthermore, because an organic solvent is used to form the release layer, special explosion-proof equipment is required, and exhaust treatment of the dried organic solvent is also required in addition to that in the example.

As shown in Table 2, in Examples 1 to 5, release films were obtained that easily achieved both releaseability and wettability of the release layer, and exhibited good coating uniformity and recyclability of the release layer. In contrast, in Comparative Examples 1 to 3, where the molecular weight of the silicone was large, coating uniformity deteriorated, ceramic sheet release tended to become severely peeled, and recyclability also deteriorated. In Comparative Examples 4 and 5, where the release layer was formed offline using a solvent-type coating solution and a large molecular weight silicone was used, recyclability deteriorated. In particular, in Comparative Example 5, the adhesion of the release layer decreased, making it difficult to achieve both releaseability and wettability of the release layer.

The release film of the present invention has high uniformity and peelability of the release layer, relatively good wettability, is easy to use as a film for various processes, is recyclable, reduces the environmental burden, and has extremely high industrial value.

Claims (6)

A release film comprising a base film and a release layer formed by reacting and solidifying an aqueous coating composition,
The aqueous coating composition comprises an alkenyl group-containing silicone having two or more alkenyl groups and Q units represented by SiO₄ _/2 in its molecule, with a number average molecular weight of 1,000 or more and less than 10,000, and an Si-H group -containing silicone having two or more Si-H groups in its molecule, with a number average molecular weight of 1,000 or more and less than 5,000.
The alkenyl group-containing silicone has a Q unit content of 0.5 mol% or more and 30 mol% or less, when all silicon atoms, including terminals within the molecule, are considered to be 100 mol%.
The aqueous coating composition contains 1 to 50 parts by mass of the Si-H group-containing silicone per 100 parts by mass of the alkenyl group-containing silicone.
Release film. The release film according to claim 1, wherein the alkenyl group-containing silicone is represented by the following general formula (I).
(In general formula (I), ^R1 may be the same or different alkenyl group having 2 to 8 carbon atoms, or a monovalent hydrocarbon group having 1 to 16 carbon atoms including an alkyl group or aryl group, and one or more of the ^R1s bonded to the silicon atom represented by [SiO] _b1 are alkenyl groups having 2 to 8 carbon atoms, ^R2 may be the same or different monovalent hydrocarbon group having 1 to 16 carbon atoms including an alkyl group or aryl group, and ^Y1 may be the same or different represented by general formula (Ia).
(In general formula (Ia), ^R1 is the same as ^R1 in general formula (I), and may be identical or different.)
In the entire general formula (I) containing ^Y1 , when all silicon atoms, including terminal atoms, are considered to be 100 mol%, a1 is between 50 mol% and 98 mol%, b1 is between 0 mol% and 10 mol%, c1 is between 0.5 mol% and 30 mol%, and d1 is between 0 mol% and 50 mol%. In the entire general formula (I) containing ^Y1 , two or more of ^R1 are alkenyl groups having 2 to 8 carbon atoms. The release film according to claim 1 or 2, wherein the Si-H group-containing silicone is represented by the following general formula (II).
(In general formula (II), ^R3 is a monovalent hydrocarbon group having 1 to 16 carbon atoms, which may be the same or different alkyl or aryl group, and when a2 + b2 is 100 mol%, a2 is 30 mol% to 90 mol%, and b2 is 10 mol% to 70 mol%.) The release layer is formed by applying the aqueous coating composition to a substrate film before crystal orientation is completed, stretching it in at least one direction, and then heat-treating it to complete the crystal orientation, as described in any one of claims 1 to 3. The release film according to any one of claims 1 to 4, wherein the base film is a polyester film. The release film according to any one of claims 1 to 5, wherein the release film is a release film for multilayer ceramic capacitors or a release film for resin sheets.