JP7626974B2 - Release Film - Google Patents

Description

The present invention relates to a release film having a base film and a release layer.

Traditionally, release films have been used to protect the adhesive surfaces of adhesives, glues, and drug patches, or as supports for resin sheets containing curable resins. In recent years, there has been particularly strong demand for them as carrier films when forming green sheets for multilayer ceramic capacitors (hereinafter referred to as "green sheets").

Conventionally, such release films have been made by providing a release layer made of an addition polymerization cured product or condensation polymerization cured product of polydimethylsiloxane on at least one side of a plastic film. These cured products have the advantages of being non-adhesive, having excellent release properties, and excellent thermal stability. However, because the surface free energy of the release layer is low, it has poor wettability with the coating raw materials, and is prone to coating defects due to poor wettability in the resulting resin layer, etc. (hereinafter referred to as the "peeled layer"). Therefore, there is a demand for a release film that has excellent wettability and peelability when forming the peeled layer.

In response to these issues, Patent Document 1 proposes a release film having a release layer crosslinked by an addition reaction between an organopolysiloxane having a hexenyl group and an organohydrogenpolysiloxane having a SiH group, in order to improve the wettability of the surface of the release layer. However, the coating uniformity and adhesion of the release layer to the substrate were not improved, making it necessary to provide an intermediate layer between the substrate and the release layer.

In addition, Patent Document 2 proposes a release film having a release layer obtained by reactively solidifying an aqueous coating composition containing two types of trialkoxysilanes, as a release film in which the release layer can be uniformly applied and formed without providing an intermediate layer on the substrate.

As a technique for controlling the reactivity of reactive silicones, Patent Document 3 proposes an aqueous dispersion of an alkenyl group-containing silicone, an aqueous dispersion of a silicone having a hydrogen atom directly bonded to a Si atom represented by a SiH group, and a release film provided with a release layer formed by curing a coating composition containing a crosslinking reaction inhibitor and a platinum-based catalyst.

JP 2012-6213 A JP 2019-55567 A JP 2014-83697 A

In recent years, there has been a demand for thinner materials that make up electronic components, such as green sheets, and high peelability (easy peelability) is required. In particular, further thinning of green sheets has been considered recently, and there is a demand for preventing damage to the green sheets when peeling and improving the recovery rate. In addition, as green sheets become thinner, foreign matter from the release layer becomes more of a problem than ever before, and there is a demand for reducing transfer to the green sheets.

In response to such problems, the inventors have found that in the technology of Patent Document 2 or Patent Document 3, depending on the amount of unreacted functional groups remaining and the type and amount of catalyst or surfactant, the release layer may take on a surface charge, which may cause foreign matter adhering to the release layer to be transferred to the green sheet. In other words, with the demand for even thinner green sheets, there is room for further improvement in the technology of Patent Document 2 or Patent Document 3 from the perspective of reducing the amount of transfer of foreign matter originating from the release layer.

The object of the present invention is to solve these problems by providing a release film that allows for uniform application of a release layer onto a substrate film, reduces the number of adhering foreign bodies, and has excellent peelability with respect to the layer to be peeled off.

As a result of intensive research into how to achieve this goal, the inventors discovered that by adding appropriate amounts of a silane coupling agent, a platinum-based catalyst, a surfactant, etc., it is possible to control the surface zeta potential of the release layer while maintaining good uniformity and releasability in the coating formation of the release layer, and that by controlling this within a predetermined range, it is possible to reduce the number of adhering foreign matter, which led to the completion of the present invention. In other words, 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 contains water, a reactive silicone, a silane coupling agent, a platinum-based catalyst, and a surfactant;
The release layer has a surface zeta potential of −60 to 0 mV.

[2] The release film according to [1], wherein the reactive silicone includes a silicone having an alkenyl group and a silicone having a SiH group.

[3] The release film according to [2], in which the content of the platinum catalyst is 10 to 800 ppm relative to the mass of the alkenyl group-containing silicone.

[4] The release film according to any one of [1] to [3], wherein the silane coupling agent includes a silane coupling agent having an alkenyl group and a silane coupling agent having an epoxy group.

[5] The release film according to any one of [1] to [4], wherein the surfactant is a nonionic surfactant, and the content of the surfactant is 2 to 20 mass % based on the total solid mass of the release layer.

[6] The release film according to any one of [1] to [5], wherein the base film is a polyester film, and the surface zeta potential of the surface on which the release layer is not provided is -40 to -30 mV.

[7] The release film according to any one of [1] to [6], which is used for forming a ceramic green sheet.

According to the present invention, it is possible to uniformly coat and form a release layer on a base film, reduce the number of adhering foreign matters, and provide a release film that has excellent peelability with respect to the layer to be peeled off.

Although the details of why such an effect is obtained are not clear, it is believed that the silane coupling agent enhances the adhesion of the release layer to the substrate film, and the surfactant improves the coatability and dispersibility of the aqueous coating composition on the substrate film, making it possible to uniformly coat and form the release layer on the substrate film. By adjusting the amount of such components and the amount of platinum-based catalyst added, the amount of unreacted functional groups, etc., changes, which makes it possible to change the surface zeta potential of the release layer, and it is believed that by controlling this within a specified range, the surface charge can be reduced and the number of attached foreign matter can be reduced. At the same time, the surface free energy, etc. are appropriately controlled, which is believed to result in excellent peelability for the layer to be peeled off.

The present invention will be described in detail below.

[Release film]
The release film of the present invention has a base film 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 a reactive silicone and a silane coupling agent that can react with each other, so it is not easy to identify the structure of the resulting polymer and to specify a claim based on it, and there are impractical circumstances. For this reason, the release film of the present invention is specified in the form of a product-by-process claim.

[Base film]
The substrate film in the present invention is not particularly limited, but examples thereof include sheets or films made of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polycarbonate, polyethylene, and polypropylene, polystyrene triacetyl cellulose, acrylic, polyimide, etc. Among them, films made of polyesters are preferred from the viewpoints of excellent mechanical properties and heat resistance, and a good balance between these properties and price. The following description will be given taking the case of polyester film as an example, but even when other resin films are used, the copolymerization components, blend components, additives, film manufacturing method, laminate structure, etc. are the same as those described below.

As the polyester film, known polyester films can be used, including known polyesters such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate), and polyethylene naphthalate. Among these, polyethylene terephthalate is particularly preferred because it has a good balance between mechanical properties and moldability.

Each of the above polyesters may be a homopolymer, a copolymer with one of these polyesters as the main component, or a blend. Here, the "main component" is 80 mol% or more based on the number of moles of the repeating structural unit of the polyester. The proportion of the main component is preferably 85 mol% or more, and more preferably 90 mol% or more. The copolymerization component or blend component is 20 mol% or less, preferably 15 mol% or less, and more preferably 10 mol% or less, based on the number of moles of the repeating structural unit of the polyester.

The polyester film may contain lubricant particles, colorants, antistatic agents, and antioxidants, as long as the object of the present invention is not impaired. When surface flatness is required, it is preferable that the film does not substantially contain lubricant particles.

Polyesters are produced by known methods, such as an esterification reaction or transesterification reaction to obtain a polyester with a low degree of polymerization, followed by the use of a polymerization catalyst to increase the degree of polymerization.

Polyester films can also be obtained by known methods, and either a sequential stretching method or a simultaneous biaxial stretching method can be used. For example, polyester can be extruded in a molten state from the die of an extruder into a sheet, the resulting sheet is cooled and solidified to form an unstretched polyester film, and the unstretched polyester film obtained is stretched in the film-forming direction and the width direction. When the polyester film has a laminated structure, for example, a polyester for layer A and a polyester for layer B are prepared, laminated in a molten state, and co-extruded from a die into a sheet, and then film-formed according to the above-mentioned method.

As the polyester film, a film that does not contain a lubricant is preferred in terms of surface flatness, but a film that contains a lubricant, for example, inorganic fine particles such as calcium carbonate, kaolin, silica, titanium oxide, etc. and/or precipitated fine particles of catalyst residue, etc., to control the surface roughness may also be used. Preferably, a base film can be used that has a smooth layer that does not contain a lubricant on the surface on which the release layer is to be provided, and a rough surface layer that contains a lubricant on the back side to control the surface roughness.

This configuration allows both surface smoothness and slipperiness to be achieved. In the present invention, "not containing particles" specifically means that the particle content is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.05% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.005% by mass or less, based on the mass of the polyester film.

There are no particular limitations on the thickness of the base film, but from the standpoint of transportability and strength as a carrier film, cost, etc., a thickness of 10 to 250 μm is preferred, 15 to 100 μm is more preferred, and 20 to 50 μm is even more preferred.

In the present invention, the surface zeta potential of the surface on which the release layer is not provided is also preferably within a specified range from the viewpoint of preventing the adhesion of foreign matter to the release layer during film transport from being transferred thereto, and can be adjusted by the surface zeta potential of the base film used, etc. The surface zeta potential of the surface on which the release layer is not provided is preferably -50 mV or more, and more preferably -40 to -30 mV.

In order to reduce the surface zeta potential of the substrate film, it is possible to add an antistatic agent to the substrate film or to provide an antistatic layer on the side opposite the release layer.

In addition, the release layer forming surface to which the aqueous coating composition is applied can be surface-treated or provided with an easy-adhesion layer in order to enhance adhesion to the release layer. Examples of surface treatments include plasma treatment, corona discharge treatment, ultraviolet treatment, flame treatment, and electron beam/radiation treatment. Examples of easy-adhesion layers include layers that contain the same resin as the base film and further contain antistatic agents, pigments, surfactants, lubricants, antiblocking agents, etc. However, in the present invention, since the aqueous coating composition used for the release layer contains a silane coupling agent, the release layer can have sufficient adhesion to the base film even without providing an easy-adhesion layer, etc.

[Release layer]
The release layer in the present invention is obtained by reacting and solidifying an aqueous coating composition. The aqueous coating composition contains water, a reactive silicone, a silane coupling agent, a platinum catalyst, and a surfactant.

[Reactive silicone]
The reactive silicone may be any silicone that undergoes a curing reaction in the presence of a silane coupling agent and a platinum-based catalyst, and examples of the reactive silicone include reactive silicone oils, modified silicones, and reactive silicone oligomers having reactive functional groups on a side chain, one end, or both ends.

Reactive silicones can exhibit excellent releasability due to structural units such as dimethylsiloxane, and the presence of reactive functional groups allows them to form crosslinked structures and to have high molecular weights. Examples of reactive functional groups include alkenyl groups, SiH groups, epoxy groups, amino groups, carboxyl groups, alcohol groups, and alkoxy groups.

It is possible to use only one type of reactive silicone as long as it undergoes a curing reaction in the presence of a silane coupling agent and a platinum-based catalyst, but it is preferable to use two or more types of reactive silicones that have reactive functional groups that react with each other. Among these, a combination of an alkenyl group-containing silicone and a SiH group-containing silicone is preferable from the viewpoint of being able to control the surface zeta potential of the release layer within a predetermined range while exhibiting good releasability.

(Alkenyl Group-Containing Silicone)
The alkenyl group-containing silicone can preferably have a number average molecular weight of 10,000 to 30,000. The number average molecular weight is preferably 15,000 to 25,000. This makes it possible to suppress the generation of silicone aggregates while providing excellent mold releasability.

The alkenyl group-containing silicone is exemplified by organopolysiloxanes having a structural unit represented by the following general formula (I): In addition to this structural unit, it is preferable to have another structural unit represented by the following general formula (I) in which a is 0 and b is 2.
R ¹ _a R ² _b SiO _(4-ab)/2 ...(I)
(In formula (I), ^R1 is an alkenyl group having 2 to 8 carbon atoms, ^R2 is a monovalent saturated hydrocarbon group having 1 to 16 carbon atoms selected from an alkyl group or an aryl group, a is an integer of 1 to 3, b is an integer of 0 to 2, and a+b≦3 is satisfied.)
The alkenyl group-containing silicone may be either a linear or branched structure, may be partially cross-linked, or may be a mixture of these. Examples of the alkenyl group having 2 to 8 carbon atoms represented by ^R1 include vinyl, allyl, butenyl, pentenyl, and hexenyl groups, and among these, vinyl is particularly preferred. Examples of the alkyl group represented by ^R2 include methyl, ethyl, propyl, and butyl groups, and examples of the aryl group include phenyl and tolyl groups. Among these, it is preferred that 80 mol % or more of the substituents of ^R2 are methyl groups in terms of light release properties.

In addition, it is preferable that the silicon atoms having alkenyl groups are in the range of 0.05 to 20 mol % of the total silicon atoms in the alkenyl group-containing silicone from the viewpoint of the curing speed and pot life of the aqueous coating composition. The alkenyl group-containing silicone of the present invention can be produced by a known method.

(SiH Group-Containing Silicone)
An example of a silicone having a hydrogen atom directly bonded to a Si atom represented by a SiH group (hereinafter sometimes referred to as a SiH group-containing silicone) is an organohydrogenpolysiloxane having a structural unit represented by the following general formula (II): In addition to this structural unit, it is preferable to have another structural unit in which d is 0 and c is 2 in the following general formula (II).
R ³ _c H _d SiO _(4-c-d)/2 ...(II)
(In formula (II), ^R3 is a monovalent saturated hydrocarbon group having 1 to 16 carbon atoms selected from an alkyl group or an aryl group, c is an integer of 0 to 2, d is an integer of 1 to 3, and c+d≦3.)
The SiH group-containing silicone may have either a linear structure or a branched structure. Examples of the alkyl group represented by ^R3 include methyl, ethyl, propyl, and butyl groups, and examples of the aryl group include phenyl and tolyl groups. In particular, it is preferable that 50 mol % or more of the substituents of ^R3 are methyl groups in terms of light releasability.
From the viewpoint of curing properties, it is preferable that the SiH group-containing silicone has at least 3, and preferably 5 or more, hydrogen atoms bonded to silicon atoms in one molecule of the silicone. The SiH group-containing silicone can be produced by a known method.

(Ratio of Number of SiH Groups to Number of Alkenyl Groups)
The ratio of the number of SiH groups to the number of alkenyl groups in the aqueous coating composition (number of SiH groups/number of alkenyl groups) is preferably in the range of 1.0 to 2.0 from the viewpoint of reducing unreacted reactive functional groups and controlling the surface zeta potential of the release layer within a predetermined range.

(Reactive Silicone Content)
In the aqueous coating composition, the total amount of the alkenyl group-containing silicone solid content and the SiH group-containing silicone solid content is preferably 70% by mass or more, more preferably 80 to 97% by mass, based on the solid content mass of the composition. Here, the silicone solid content refers to the amount excluding the aqueous solvent, and the solid content mass of the aqueous coating composition refers to the total amount of the solid content of each additive. When the total amount of the silicone solid content is equal to or more than the lower limit, the area covered with silicone on the substrate film surface becomes sufficient, the peeling force can be reduced, and the peeling force is less likely to become non-uniform.

[Silane coupling agent]
Silane coupling agent is used to improve the adhesion of release layer to substrate film, and is an alkoxysilane compound having a reactive group that can chemically bond with organic material. In the present invention, it is preferable to use a combination of silane coupling agent X containing alkenyl group and silane coupling agent Y having other reactive functional group. By combining both, the adhesion between release layer and substrate film can be further improved.
The content of the silane coupling agent is, from the viewpoint of controlling the surface zeta potential of the release layer within a predetermined range while increasing the adhesion of the release layer to the substrate film, preferably 0.3 to 33 mass %, more preferably 0.5 to 30 mass %, and even more preferably 1 to 15 mass %, relative to the total amount of silicone solids contained in the aqueous coating composition.

[Silane coupling agent X]
The silane coupling agent X contains an alkenyl group, and is believed to improve adhesion mainly by reacting with reactive silicone. Examples of the alkenyl group include lower (especially C2-4) alkenyl groups such as vinyl, 1-propenyl, isopropenyl, 2-methyl-1-propenyl, 1-butenyl, 2-butenyl, and 3-butenyl, with the vinyl group being preferred.

The silane coupling agent X may be of the monoalkoxy, dialkoxy or trialkoxy type depending on the number of alkoxy groups, but from the viewpoint of reactivity, a trialkoxy type silane coupling agent is preferred. Examples of the alkoxy group include a methoxy group and an ethoxy group, but from the viewpoint of reactivity, a methoxy group is preferred.

[Silane coupling agent Y]
Silane coupling agent Y has other reactive functional groups, and is considered to improve adhesion mainly by reacting with the surface of substrate film.Reactive functional groups include epoxy groups, amino groups, isocyanate groups, and mercapto groups, and from the viewpoint of reactivity with polyester and the like, epoxy groups and isocyanate groups are preferred.Reactive functional groups may be bonded to silicon atoms via spacer groups, and the spacer groups include alkylene groups, oxyalkylene groups, aminoalkylene groups, arylene groups, etc.

The silane coupling agent Y may be of the monoalkoxy, dialkoxy or trialkoxy type depending on the number of alkoxy groups, but from the viewpoint of reactivity, a trialkoxy type silane coupling agent is preferred. Examples of the alkoxy group include a methoxy group and an ethoxy group, but from the viewpoint of reactivity, a methoxy group is preferred.

[Mole ratio of silane coupling agent]
The molar ratio (X/Y) of the silane coupling agent X to Y is preferably 55/45 to 85/15, more preferably 60/40 to 80/20, and even more preferably 65/35 to 75/25. When the molar ratio is within the above range, the balance between the releasability and the zeta potential of the release layer is good, making it easier to achieve the desired wettability, releasability, and number of attached foreign matter.

[Platinum-based catalyst]
In the aqueous coating composition, a platinum-based catalyst is used to promote the reaction of reactive silicones, for example, the addition reaction between alkenyl-group-containing silicones and SiH-group-containing silicones.

Known platinum catalysts can be used, such as platinum chloride and chloroplatinic acid. Taking into account dispersibility in silicone, the platinum catalyst may be 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt catalyst), which can be dispersed simultaneously with the silicone being emulsified to ensure uniform dispersion.

The amount of platinum catalyst is preferably in the range of 10 to 800 ppm of platinum element mass relative to the mass of alkenyl group-containing silicone. By setting it in such a range, silicone can be sufficiently cured, and the surface zeta potential of the release layer can be easily controlled within a predetermined range. For example, it is known that the presence of unreacted alkenyl groups increases the zeta potential (and the charge amount), and the reactivity (curability) of the release layer can be improved by adding the amount of platinum catalyst, while the target zeta potential can be achieved. In addition, the generation of silicone aggregates can be suppressed, and a release film with excellent surface properties can be obtained. From this viewpoint, the amount of platinum catalyst is preferably 600 ppm or less, more preferably 500 ppm or less, even more preferably 200 ppm or less, particularly preferably 120 ppm or less, and most preferably 100 ppm or less. From the above viewpoint, it is preferably 15 ppm or more, more preferably 20 ppm or more, even more preferably 25 ppm or more, and particularly preferably 80 ppm or more.

[Surfactant]
A surfactant is added to the aqueous coating composition for providing the release layer in order to promote wetting of the substrate film. Examples of such surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, etc., and it is also possible to use one or more of these. However, from the viewpoint of inhibiting the curing reaction of the silicone component and the stability of the aqueous coating composition, it is preferable to use a nonionic surfactant.

From the viewpoint of emulsifying and dispersing power and stability of the aqueous dispersion, nonionic surfactants having an HLB value in the range of 8 to 18 are preferred. Examples of nonionic surfactants include at least one selected from alkylene oxide adducts such as alkylene oxide adducts of higher alcohols or higher fatty acids, esters of alkylene oxide adducts of higher fatty acids and alcohols, alkylene oxide adducts of alkanolamides, alkylene oxide adducts of sorbitan esters, and alkylene oxide adducts of higher fatty acid glycerides. Here, the HLB value is a value calculated by Griffin's formula.

Examples of alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide, and one or more of these may be used. When more than one is used, the addition form may be block or random, 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, polyoxyethylene tridecyl ether, etc. are preferred.

When an anionic surfactant (negative ion system) is added, the ion concentration increases as the amount added increases, and the zeta potential tends to increase (in the negative direction). Conversely, cationic surfactants (cations) can act to make the zeta potential positive, and can be used to reduce the absolute value of the zeta potential.

The surfactant content is preferably 0.1 to 20% by mass, more preferably 2 to 15% by mass, relative to the mass of the release layer (total solid mass). If it is equal to or higher than the lower limit, the aqueous coating composition will have good wettability to the film substrate, a uniform release layer will be formed, the release properties will be good, and the zeta potential will be stable. If it is equal to or lower than the upper limit, aggregation of the surfactant itself will be suppressed, a uniform release layer will be formed, the release properties will be good due to the appropriate surface free energy, and the zeta potential will be an appropriate value.

[Aqueous Solvent]
The aqueous coating composition contains an aqueous solvent that contains water. By using an aqueous solvent, a release layer can be formed without using explosion-proof equipment and recovery equipment that are required for organic solvents during the film formation process.

(Crosslinking reaction inhibitor)
In the present invention, in order to suppress the activity of the platinum-based catalyst at room temperature, it is preferable that the aqueous coating composition contains a crosslinking reaction inhibitor. Such a crosslinking reaction inhibitor is preferably a crosslinking reaction inhibitor having an ethynyl group. The crosslinking reaction inhibitor having an ethynyl group is not particularly limited as long as it has an ethynyl group, but since the present invention employs an aqueous coating composition, it is preferable to use a crosslinking reaction inhibitor having an ethynyl group and a hydroxyl group, such as 1-ethynylcyclohexanol, in view of the balance between solubility in water and coordination ability to platinum, and the boiling point.

The content of the crosslinking reaction inhibitor is preferably 10 ppm or more, more preferably 50 ppm or more, based on the mass of the coating liquid used to form the release layer. This tends to reduce the number of aggregates. In addition, from the viewpoint of suitably suppressing the silicone curing reaction, the content of the crosslinking reaction inhibitor is preferably 500 ppm or less, more preferably 400 ppm or less, even more preferably 300 ppm or less, particularly preferably 150 ppm or less, and most preferably 100 ppm or less.

(Other ingredients)
Other additives such as antistatic agents, ultraviolet absorbers, pigments, colorants, organic or inorganic particles, lubricants, and antiblocking agents can be mixed into the aqueous coating composition within the range that does not impair the effects of the present invention.

(Preparation of Silicone Water Dispersion)
When preparing each silicone water dispersion that is the raw material of the aqueous coating composition, there can be mentioned a method of emulsifying using the above-mentioned silicone component, aqueous solvent and surfactant.These components can be emulsified by a known method, for example, there can be mentioned a method of mechanically emulsifying the silicone and surfactant that are prepared in advance, and other components as required, in the aqueous medium using a stirring device such as homogenizer, azihomomomixer, ultra planetary mixer, etc.

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

[Physical properties of release layer]
The release film of the present invention is characterized in that the surface zeta potential of the release layer measured by the streaming potential method is −60 to 0 mV with respect to a (polystyrene) monitor particle dispersion. The surface zeta potential is preferably −55 to 0 mV, more preferably −50 to 0 mV. If the zeta potential exceeds −60 mV, foreign matter such as polymer degradation products floating in the tenter during film production or during transport is likely to adhere, and defects in the green sheet and the like are likely to increase. In addition, if the surface zeta potential exceeds 0 mV and becomes a positive potential, when the film is made into a roll film, it is likely to adhere to a surface on which the release layer is not provided, and the amount of charge increases due to friction between the films caused by vibration during transport, which may deteriorate the handling properties. In addition, the zeta potential of an untreated polyester film is generally −40 to −30 mV.
The surface zeta potential can be controlled by changing the amount of platinum catalyst added, the amount of silane coupling agent added, the molar ratio of silane coupling agents X and Y, the type and amount of surfactant added, etc. When the amount of unreacted groups such as vinyl groups and SiH groups increases, the absolute value of the surface zeta potential tends to increase.

The thickness of the release layer is preferably 5 nm to 100 nm, more preferably 5 nm to 80 nm, and even more preferably 10 nm to 50 nm. If the thickness of the release layer is 5 nm or more, the surface of the substrate film can be completely covered, making it easier to ensure peelability. Furthermore, if the thickness of the release layer is 100 nm or less, the release film becomes easier to handle during roll-to-roll transport, and the amount of heat required to cure the coating film is not too large.

From the viewpoint of wettability of the layer to the coating material and peelability of the layer to be peeled, the surface free energy of the release layer is preferably 10 mN/m or more and 35 mN/m or less, and more preferably 15 mN/m or more and 30 mN/m or less.

[Application]
The release film of the present invention can be used for the purpose of protecting the adhesive surface of a pressure sensitive adhesive, a bonding agent, a drug patch, etc., or for the purpose of protecting the curing reactivity and formability of a curable resin, such as a urethane resin, an epoxy resin, an unsaturated polyester resin, etc. It can also be used as a support for various resin sheets, for example, as a carrier film when forming green sheets for a multilayer ceramic capacitor, a ceramic multilayer wiring board, etc.

[Method of producing release film]
The method for producing the release film is not particularly limited, but the release layer can be formed by applying an aqueous coating composition to at least one surface of a substrate film, followed by drying, reaction, and solidification.

The coating may be carried out in a normal coating process, that is, in a process in which the polyester film is coated separately from the manufacturing process of the film. However, since this process is prone to involving dirt, dust, etc., it is desirable to carry out the coating in a clean atmosphere. From this viewpoint, coating during the polyester film manufacturing process is preferred. In particular, from the viewpoint of adhesion to the polyester film, it is preferable to apply the aqueous coating composition to the polyester film before the crystal orientation is completed during this process.

Here, polyester film before the crystal orientation is completed includes unstretched film made by thermally melting polyester and forming it into a film, uniaxially stretched film made by orienting unstretched film in either the machine direction (lengthwise) or the cross direction (widthwise), and film oriented by low-magnification stretching in both the machine direction and the cross direction (biaxially stretched film before the orientation crystal orientation is completed by finally re-stretching in the machine direction or the cross direction).

Any known coating method can be used as the coating method. For example, kiss coating, bar coating, die coating, reverse coating, offset gravure coating, Mayer bar coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, and curtain coating can be used alone or in combination.

The polyester film coated with the aqueous coating composition and before completing the crystal orientation is dried and then guided to processes such as stretching and heat setting. For example, a uniaxially longitudinally stretched polyester film coated with the aqueous coating composition is guided to a tenter for transverse stretching and heat setting. During this time, the aqueous coating composition is dried and reacts and solidifies (thermal crosslinking).

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The methods for evaluating physical properties and the like in the following examples are as follows.

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

(2) Thickness of release layer After cutting the release film into small triangular pieces, a Pt (platinum) layer with a thickness of 2 nm was formed on the surface of the release layer by coating. The obtained sample was fixed in a multi-axis embedding capsule, embedded with epoxy resin, and sliced in a direction perpendicular to the surface direction of the film using a microtome ULTRACUT-S to obtain an ultra-thin sample with a thickness of 50 nm. Next, the obtained ultra-thin sample was placed on a grid and steam-dyed with 2% osmic acid at 60 ° C. for 2 hours. Using the ultra-thin sample after steam dyeing, the film cross section was observed with a transmission electron microscope LEM-2000 under an acceleration voltage of 100 kv, and the thickness of the release layer was measured. The measurement was performed at any 10 points, and the average value was taken as the thickness of the release layer (unit: nm).

(3) Coating Uniformity of Release Layer A release film was cut into an A4 size, and the release layer surface was visually observed using a fluorescent lamp and a halogen light to compare the number of aggregated coating defects, and the results were evaluated according to the following criteria.
⊚ (Excellent): No coating defects with a major axis of 0.5 mm or more are observed per 1 ^m2 of the release layer surface.
◯ (Good): No coating defects with a major axis of 1.0 mm or more are observed on 1 ^m2 of the release layer surface.
Δ (Moderate): No coating defects with a major axis of 1.5 mm or more are observed on 1 ^m2 of the release layer surface.
× (poor): One or more coating defects having a major axis of 2.0 mm or more are observed per 1 ^m2 of the release layer surface.

(4) Surface Free Energy The static contact angles of the release layer surface of the film sample, which had been conditioned for 24 hours under conditions of 23°C and 65% RH, with water, methylene iodide, and n-hexadecane were measured using an automatic contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd.). Measurements were performed five times for each liquid sample, and the average value was taken as the contact angle of the film sample. The surface free energy of the release layer surface was calculated from the following Fowkes' expanded formula (I) using the surface tension and surface tension component values of each liquid sample (Table 1).
γ _S = γ _S ^d + γ _S ^p + γ _S ^h ...(1)
(In the above formula, γ _S ^d represents a dispersion component, γ _S ^p represents a polar component, and γ _S ^h represents a hydrogen bond component.)

(5) Measurement of Zeta Potential The surface zeta potential of the release layer of the release film was measured by electrophoretic light scattering using a Zetasizer Nano ZS manufactured by Malvern Panalytical. The release film was cut to the size of the sample holder (about 4 mm x 5 mm) of the attached flat plate zeta potential measurement cell, and the surface opposite to the release layer was attached to the sample holder to be used as a measurement sample. A polystyrene latex suspension with a zeta potential suppressed to approximately 0 mV as tracer particles (standard particles) was placed in the flat plate zeta potential measurement cell, and the sample holder with the sample set was immersed in the cell. An electric field was applied to the tracer particles, and the zeta potential of the sample surface was obtained from the mobility of the tracer particles, which changes depending on the state of the sample surface. The measurement conditions were water temperature: 25 ° C., refractive index: 1.3328, viscosity: 0.8878 cP, dielectric constant: 78.3, and the average value of N = 3 was taken as the zeta potential (mV).

To measure the surface zeta potential on the back side of the release film (the side opposite the release layer), the sample was set so that the back side was the surface, and the surface zeta potential was measured in the same manner as above.

(6) Evaluation of the number of adhering foreign objects Fifty sheets of release film with a size of 50 mm square were laminated, and the air between the film layers was removed by vacuum suction to obtain a laminated film as a measurement sample. The protruding foreign objects observed on the surface of this laminated film were counted, and the value calculated by converting the total area of the laminated film to a value per unit area was taken as the number of adhering foreign objects (pieces/100 ^m2 ). If the number of defects was 0.1 pieces/100 ^m2 or more, the electrical characteristic failure rate would be high when the MLCC chip was manufactured. The main types of adhering foreign objects were PET oligomers, PET shavings, nylon, and cellulose.
◎ (Excellent): The number of attached foreign matter is less than 0.03 pieces/100 ^m2 ○ (Good): The number of attached foreign matter is 0.03 pieces/100 ^m2 or more and less than 0.05 pieces/100 m2 △ (Moderate): The number of attached foreign matter is 0.05 pieces/100 ^{m2 or} more and less than 0.1 pieces/100 ^m2 × (Poor): The number of attached foreign matter is 0.1 pieces/100 ^m2 or more (7) Evaluation of peel strength of resin layer On the surface on which the release layer of the prepared release film was formed, a solution obtained by dissolving polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., BM-2) in a toluene-ethanol 7:3 (mass ratio) mixture was applied using an applicator so that the thickness of the resin layer was 3.0 μm, and then the surface was left at room temperature for 20 minutes and then dried at 70 ° C. to form a resin layer. The formed resin layer was attached and fixed to a SUS plate with adhesive tape attached, and the release film was peeled off at a peel angle of 90 degrees, a peel speed of 300 mm/min, and a sample width of 25 mm, and the peel resistance at that time was measured. If the peel strength exceeds 10 g/25 mm, the resin layer breaks (the resin layer remains on the SUS plate side), which is problematic in practical use.
⊚ (Excellent): peel strength less than 3 g/25 mm ◯ (Good): peel strength 3 g/25 mm or more and less than 7 g/25 mm Δ (Moderate): peel strength 7 g/25 mm or more and 10 g/25 mm or less × (Poor): peel strength exceeds 10 g/25 mm or the resin layer breaks.

[Example 1]
Polyethylene terephthalate (η=0.64 dl/g, Tg=78° C.) containing 0.1% by mass of calcium carbonate particles with an average particle size of 0.7 μm as the rough surface layer and polyethylene terephthalate ((η=0.64 dl/g, Tg=78° C.)) not containing any particles as the smooth layer were laminated in a molten state to form a rough surface layer/smooth layer, extruded from the die of an extruder, cooled by a conventional method on a cooling drum to form an unstretched film, and then stretched 3.6 times in the machine direction at 80° C., after which an aqueous coating composition having the composition described below was uniformly applied to the smooth layer surface of the film by a roll coater. The coating solution of the aqueous coating composition used was one prepared within 4 hours. Next, this coated film was dried at 115°C, stretched 4.0 times in the transverse direction at 145°C, and further heat-set at 230°C for about 10 seconds to obtain a release film consisting of a biaxially stretched polyester film (total thickness 31 μm, rough surface layer thickness 7 μm, smooth layer thickness 24 μm) having a release layer (thickness 20 nm) shown in Table 1. This release film was evaluated as described above. The results are shown in Table 2.

The aqueous coating composition was prepared by using the materials shown below, each of which was composed of 100 parts by weight of an alkenyl group-containing silicone water dispersion, 12 parts by weight of an SiH group-containing silicone water dispersion, 100 ppm of a platinum catalyst relative to the amount of alkenyl group-containing silicone, 150 ppm of a crosslinking reaction inhibitor, and a total of 5% by weight of silane coupling agents X and Y relative to the total amount of silicone solids (molar ratio X:Y = 65:35). The solid content concentration of the coating liquid was diluted with water to prepare a coating liquid with a target coating thickness. This aqueous coating composition was prepared using an emulsifier (manufactured by NP Lab Co., Ltd., device name "Ultra Planetary Mixer") to prepare a coating liquid with an average emulsion particle size of 200 nm (total silicone solid content 90% by weight).

<Alkenyl Group-Containing Silicone Water Dispersion>
Using an emulsifier that can stir the entire container (manufactured by NP Labs, device name "Ultra Planetary Mixer"), mechanically emulsify raw materials that consist of 98% by mass of the silicone (number average molecular weight 15000) with alkenyl group represented by the following formula (1) and 2% by mass of polyoxyethylene lauryl ether (manufactured by Kao Corporation, product name "Emulgen 109P") as surfactant in aqueous medium, obtain an alkenyl group-containing silicone water dispersion with solid content of 20% by mass.In addition, by adjusting the stirring speed and stirring time during emulsification, the emulsion particle size is adjusted to an average particle size of 200 nm.
In formula (1), m was 2, and n was adjusted to give a number average molecular weight of 15,000.

<SiH Group-Containing Silicone Water Dispersion>
Using an emulsifier capable of stirring the entire container (manufactured by NP Labs, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by mass of silicone (number average molecular weight: 4500) having hydrogen groups represented by the following formula (2) and 2% by mass of polyoxyethylene lauryl ether (manufactured by Kao Corporation, product name "Emulgen 109P") as a surfactant are mechanically emulsified in an aqueous medium to obtain a SiH group-containing silicone water dispersion with a solid content of 10% by mass. Also, by adjusting the stirring speed and stirring time during emulsification, the emulsion particle size is adjusted to an average particle size of 200 nm.
(In formula (2), o = 30 and p = 35)
<Platinum-based catalyst>
A platinum catalyst emulsion (manufactured by Shin-Etsu Chemical Co., Ltd., product name "CATPM-10A") was adjusted to have the platinum element mass shown in Table 2.

<Crosslinking reaction inhibitor>
1-Ethynylcyclohexanol (Alfa Lancaster) was used.

<Silane coupling agent X>
Vinyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name "KBM-1003") was used.

<Silane coupling agent Y>
3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name "KBM-403") was used.

[Examples 2 to 16]
A release film was produced under the same conditions as in Example 1, except that the composition of the aqueous coating composition in Example 1 was changed to that shown in Table 2, and the above-mentioned evaluation was carried out. The results are shown in Table 2. The number average molecular weight of the alkenyl group-containing silicone was adjusted by changing n in formula (1).

[Comparative Examples 1 to 2]
In Example 1, release films were produced under the same conditions as in Example 1, except that the amount of the platinum-based catalyst added in the aqueous coating composition was changed as shown in Table 2, and the above-mentioned evaluation was carried out. The results are shown in Table 3.

[Comparative Examples 3 to 4]
In Example 1, the release film was produced under the same conditions as in Example 1, except that the amount of the silane coupling agent added in the aqueous coating composition was changed as shown in Table 2, and the above-mentioned evaluation was performed. The results are shown in Table 3.

[Comparative Examples 5 to 6]
In Example 1, except that the molar ratio of the silane coupling agent X and Y in the aqueous coating composition was changed as shown in Table 2, the release film was produced under the same conditions as in Example 1, and the above-mentioned evaluation was carried out. The results are shown in Table 3.

[Comparative Examples 7 to 8]
Release films were prepared under the same conditions as in Example 1, except that the amount of surfactant added to the aqueous coating composition was changed as shown in Table 2, and the above-mentioned evaluations were carried out. The results are shown in Table 3.

[Comparative Example 9]
A release film was prepared under the same conditions as in Example 1, except that no surfactant was added to the aqueous coating composition as shown in Table 2, and the above-mentioned evaluation was carried out. The results are shown in Table 3.

As shown in Table 2, in Examples 1 to 16, by adding appropriate amounts of silane coupling agents, platinum-based catalysts, surfactants, etc., it was possible to maintain good coating uniformity and peelability while controlling the surface zeta potential of the release layer within a specified range, thereby reducing the number of adhering foreign particles.

In contrast, as shown in Table 3, in Comparative Example 1, where a small amount of platinum-based catalyst was added, the absolute value of the surface zeta potential increased due to an increase in unreacted groups, and an increase in the number of attached foreign particles and an increase in peel strength were observed. Also, in Comparative Example 2, where an excessive amount of platinum-based catalyst was added, the absolute value of the surface zeta potential increased due to an increase in agglomerated coating defects, and an increase in the number of attached foreign particles was observed.

In Comparative Example 3, where a small amount of silane coupling agent was added, the absolute value of the surface zeta potential increased due to an increase in aggregated coating defects, an increase in the number of adhering foreign matter was observed, and adhesion to the substrate decreased, resulting in insufficient release action. The absolute value of the surface zeta potential increased, and an increase in the number of adhering foreign matter and an increase in peel strength were observed. In Comparative Example 4, where an excess of silane coupling agent was added, the absolute value of the surface zeta potential and surface free energy increased due to an increase in unreacted groups, and an increase in the number of adhering foreign matter and an increase in peel strength were observed.

In Comparative Example 5, where a smaller amount of silane coupling agent X was added, the absolute value of the surface zeta potential was slightly larger, an increase in the number of adhering foreign matter was observed, and adhesion to the substrate was reduced, resulting in insufficient release action. In Comparative Example 6, where an excess amount of silane coupling agent X was added, the absolute value of the surface zeta potential was larger due to an increase in unreacted groups, and an increase in the number of adhering foreign matter was observed.

In Comparative Example 7, in which a smaller amount of surfactant was added, and Comparative Example 9, in which no surfactant was added, the release layer became non-uniform, the measurement of the surface zeta potential became difficult (unstable), an increase in the number of adhering foreign matter was observed, and the release action was insufficient. In Comparative Example 8, in which an excessive amount of surfactant was added, the release layer became non-uniform, the measurement of the surface zeta potential became difficult (unstable), an increase in the number of adhering foreign matter was observed, and the release action was insufficient.

The release film of the present invention allows for the uniform application and formation of a release layer on a substrate film, reduces the amount of adhering foreign matter, has excellent peelability for the layer to be peeled off, and can be used for a variety of applications, making it extremely valuable in industry.

Claims (4)

A release film having a base film and a release layer formed by reacting and solidifying an aqueous coating composition,
The aqueous coating composition contains water, a reactive silicone, a silane coupling agent, a platinum-based catalyst, and a surfactant;
The reactive silicone includes a silicone having an alkenyl group and a silicone having a SiH group,
the content of the platinum-based catalyst is 10 to 800 ppm relative to the mass of the alkenyl group-containing silicone,
The content of the silane coupling agent is 0.3 to 33 mass% based on the total amount of silicone solids,
the surfactant is a nonionic surfactant, and the content of the surfactant is 2 to 20% by mass based on the total solid content mass of the release layer;
The release layer has a surface zeta potential of −60 to 0 mV. The release film according to claim 1 , wherein the silane coupling agent comprises a silane coupling agent having an alkenyl group and a silane coupling agent having an epoxy group. 3. The release film according to claim 1 , wherein the base film is a polyester film, and the surface zeta potential of the surface on which the release layer is not provided is −40 to −30 mV. The release film according to any one of claims 1 to 3 , which is used for forming a ceramic green sheet.