JP7803407B2 - Silicone release polyester film and its manufacturing method - Google Patents

Description

The present invention relates to a silicone release polyester film. More specifically, the present invention relates to a silicone release polyester film that has easy releasability ideal for molding ceramic green sheets used in the production of multilayer ceramic capacitors and that can prevent sheet tearing and pinholes from occurring during the peeling and lamination of ceramic green sheets, as well as a method for producing the same, and a protected object on which the silicone release polyester film is laminated.

In the manufacture of multilayer ceramic capacitors, release films are used as carrier films for molding ceramic green sheets. Polyester film is used as the base material for release films, particularly for its dimensional stability and heat resistance. In recent years, while multilayer ceramic capacitors have become smaller and larger in capacity, high reliability is required for automotive use, and there is a growing demand for improved quality ceramic green sheets.

As ceramic green sheets become thinner and more reliable, the thickness of the dried sheets is now in the range of a few microns or less. Therefore, carrier films are particularly required to have easy releasability. However, as ceramic green sheets become thinner, their rigidity decreases, and the peeling force of conventional release films can cause tears and deformation when peeling the green sheets, resulting in a higher chip defect rate. To avoid this, easy releasability is required.

Therefore, there is a demand for reducing the peel strength of release films. For example, methods have been proposed for adjusting the peel strength by controlling the crosslinking structure of silicone (see, for example, Patent Document 1). However, such methods of controlling the crosslinking structure of the release layer may require new designs for polymers or crosslinking agents with special structures, or may require stronger energy during ultraviolet or electron beam irradiation, resulting in increased costs. Release layers composed of silicone resins with and without crosslinking structures have also been proposed (see, for example, Patent Document 2). However, this method poses the problem of high costs, as the coating agent used to form the release layer uses an organic solvent, requiring large-scale organic solvent treatment equipment during coating and drying, as well as running costs for treating the evaporated organic solvent. Furthermore, there are issues with the working environment and safety, such as the risk of organic solvent explosions and fires.

Methods that do not use organic solvents have also been proposed (see, for example, Patent Document 3), but these methods have problems such as increased viscosity of the coating, making handling more difficult and making it difficult to achieve uniform coating. Also, methods using water-based silicone emulsions have been proposed (see, for example, Patent Document 4), but these methods have problems such as the type of surfactant (or emulsifier) used not being clearly specified and no reaction inhibitor being used, resulting in poor emulsion stability and making it difficult to achieve uniform coating. Thinning ceramic green sheets requires extremely high uniformity on the release layer surface, and these methods are insufficient.

Japanese Patent Application Laid-Open No. 2006-7689 Japanese Patent Application Laid-Open No. 2008-254207 Japanese Patent Application Laid-Open No. 2003-192987 Special Publication No. 2009-518499

In view of the above circumstances, the present invention aims to provide a silicone release polyester film that has excellent easy releasability and release layer (film) uniformity, a method for producing the same, and a protected object on which the silicone release polyester film is laminated.

The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that the above-mentioned problems could be solved by using a specific silicone, a catalyst for the silicone crosslinking reaction, and a crosslinking reaction inhibitor, and by applying a catalyst that maximizes crosslink density as much as possible during the release layer formation process, thereby completing the present invention.

That is, the present invention provides the following silicone release polyester film (silicone releaseable polyester film).

[1] A silicone release polyester film having a coating layer (also referred to as a "release layer" in this specification) formed on at least one surface of the polyester film using a release coating composition comprising 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 Si-H group, and an aqueous dispersion containing a platinum-based catalyst,
The amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm relative to the weight of the alkenyl group-containing silicone,
The platinum-based catalyst includes a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor,
The thickness of the coating layer is 5 nm or more and 70 nm or less.
Silicone release polyester film.

[2] The platinum element amount (P0) of the platinum-based catalyst not containing the crosslinking reaction inhibitor is 50 ppm or more and less than 400 ppm relative to the weight of the alkenyl group-containing silicone,
the platinum element amount (P1) of the platinum-based catalyst containing the crosslinking reaction inhibitor is 40 ppm or more and less than 400 ppm relative to the weight of the alkenyl group-containing silicone;
[1] The silicone release polyester film according to [1].

[3] The platinum-based catalyst contains a platinum element amount (P0) of a platinum-based catalyst that does not contain the crosslinking reaction inhibitor, and a platinum element amount (P1) of a platinum-based catalyst that contains the crosslinking reaction inhibitor,
The silicone release polyester film according to [1] or [2], wherein the ratio (P0/(P1+P0)) of the amount of platinum element (P0) in the platinum-based catalyst not containing the crosslinking reaction inhibitor to the total weight of platinum element (P1+P0) is 0.3 or more and 0.8 or less.

[4] A silicone release polyester film described in any one of [1] to [3], wherein the alkenyl group of the alkenyl group-containing silicone is a vinyl group.

[5] A silicone release polyester film described in any one of [1] to [4], which is used for molding ceramic green sheets in the production of multilayer ceramic capacitors.

The present invention also provides the following protected objects:

[6] The above-mentioned protected object, in which the silicone release polyester film described in any one of [1] to [5] is laminated on the surface of the coating layer or the surface of the release layer.

[7] The protected object of [6] is a ceramic green sheet.

The present invention also provides the following method for producing a silicone release polyester film.

[8] A method for producing a silicone release polyester film, comprising the step of forming a coating layer on at least one surface of a polyester film using a release coating composition comprising 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 Si—H group, and an aqueous dispersion containing a platinum-based catalyst,
The amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm relative to the weight of the alkenyl group-containing silicone,
The platinum-based catalyst includes a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor,
The thickness of the coating layer is 5 nm or more and 70 nm or less.
Method for producing silicone release polyester film.

By virtue of the above-described structure, the silicone release polyester film of the present invention has a moderately low peel strength and excellent release layer uniformity. The silicone release polyester film of the present invention, possessing the above-described properties, can be suitably used, for example, as a carrier film for molding ceramic green sheets used in ceramic multilayer capacitors.

In addition, since the object to be protected is laminated with a silicone release polyester film that has the above-mentioned properties, it can be used effectively when the object to be protected is, for example, a ceramic green sheet.

In addition, the method for producing silicone release polyester film of the present invention makes it possible to efficiently and easily obtain silicone release polyester film having the above-mentioned properties.

The following describes in detail the embodiments of the present invention, but the present invention is not limited to these embodiments.

<Silicone release polyester film>
The silicone release polyester film of the present invention is
A silicone release polyester film having a coating layer formed on at least one surface of the polyester film using a release coating composition comprising 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 an Si—H group, and an aqueous dispersion containing a platinum-based catalyst,
The amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm relative to the weight of the alkenyl group-containing silicone,
The platinum-based catalyst includes a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor,
The thickness of the coating layer is 5 nm or more and 70 nm or less.

[Polyester film]
For the polyester film of the present invention, any known polyester can be used as appropriate, and for example, the following polyesters can be suitably used.

(polyester)
The polyester constituting the polyester film used as the substrate film (hereinafter sometimes referred to as substrate) in the present invention is not particularly limited, and a film of a polyester commonly used as a substrate for release films can be used. Preferred are crystalline linear saturated polyesters composed of an aromatic dibasic acid component and a diol component. For example, polyethylene terephthalate, polyethylene isophthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate), polytrimethylene terephthalate, or copolymers primarily composed of these resin components are even more preferred. Of these, polyester films formed from polyethylene terephthalate are particularly preferred. The polyethylene terephthalate preferably contains 90 mol% or more, more preferably 95 mol% or more, of ethylene terephthalate repeating units, and may be copolymerized with small amounts of other dicarboxylic acid components or diol components. For example, from the standpoint of cost, those produced solely from terephthalic acid and ethylene glycol are preferred.

In addition, known additives such as antioxidants, light stabilizers, UV absorbers, and crystallization agents may be added within a range that does not impair the effects of the release film of the present invention. The polyester film is preferably a biaxially oriented polyester film due to its high bidirectional elastic modulus.

The intrinsic viscosity of the 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 0.65 dl/g or less. An intrinsic viscosity of 0.50 dl/g or more 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 allows for good cuttability when cutting to the specified product width and prevents dimensional defects. It is also preferable to thoroughly vacuum dry the raw material pellets.

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

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

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

The polyester film preferably has a thickness of 12 μm or more and 100 μm or less, more preferably 16 μm or more and 50 μm or less, and even more preferably 19 μm or more and 33 μm or less. A film thickness of 12 μm or more is preferable because there is no risk of deformation due to heat during film production, processing, or molding. On the other hand, a film thickness of 100 μm or less is preferable in terms of reducing the environmental impact because the amount of film discarded after use is not excessively large.

The polyester film substrate may be a single layer or a multi-layer structure of two or more layers. For example, the substrate film may be a polyester film having a surface layer A that is substantially free of particles with a particle size of 1.0 μm or more, and a surface layer B that contains particles. Preferably, surface layer A is substantially free of inorganic particles with a particle size of 1.0 μm or more.

In this embodiment, particles with a particle size of less than 1.0 μm and equal to or greater than 1 nm may be present in surface layer A. By having surface layer A substantially free of particles with a particle size of 1.0 μm or greater, such as inorganic particles, it is possible to reduce the possibility of defects occurring due to the particle shape in the substrate being transferred to the resin sheet.

In one aspect, surface layer A does not contain particles with a particle size of less than 1.0 μm, which more effectively prevents the particle shape in the substrate from being transferred to the resin sheet, causing defects.

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 more effectively prevents defects caused by the particle shape in the substrate being transferred to the resin sheet.

For example, it is preferable that surface layer A, which contains substantially no particles with a particle size of less than 1.0 μm, also contains substantially no particles with a particle size of 1.0 μm or more.

In this specification, "substantially free of particles" means, for example, in the case of inorganic particles less than 1.0 μm in size, that the content of inorganic elements quantified by fluorescent X-ray analysis is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit. This is because even if particles are not actively added to the film, contaminants from foreign matter or dirt adhering to the raw resin or the production line or equipment during the film manufacturing process may peel off and be mixed into the film. Furthermore, "substantially free of particles with a particle size of 1.0 μm or larger" means that particles with a particle size of 1.0 μm or larger are not actively included.

In the case of a laminated polyester film consisting of two or more layers, it is preferable that the surface opposite to the surface layer A, which contains substantially no inorganic particles, has a surface layer B, which may contain inorganic particles, etc.

In terms of the laminate structure, if the layer on the side to which the release layer is applied is Layer A, the layer on the opposite side is Layer B, and the other core layer is Layer C, the layer structure in the thickness direction can be a laminate structure such as release layer/A/B or release layer/A/C/B. Naturally, Layer C can also be a multi-layer structure. Furthermore, surface layer B can contain no inorganic particles. In that case, it is preferable to provide a coating layer containing at least inorganic particles and a binder on surface layer B to impart slip properties when winding the film into a roll.

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

In this case, the regional surface average roughness (Sa) of the film of surface layer B is preferably in the range of 1 nm to 40 nm. More preferably, it is in the range of 5 nm to 35 nm. When the total silica particles and/or calcium carbonate particles is 5,000 ppm or more and Sa is 1 nm or more, air can be uniformly released when the film is wound into a roll, resulting in a good wound shape and good flatness, making it suitable for producing ultra-thin ceramic green sheets. Furthermore, when the total silica particles and/or calcium carbonate particles is 15,000 ppm or less and Sa is 40 nm or less, the lubricant is less likely to aggregate and large protrusions are not formed, which is preferable as it ensures stable quality when producing ultra-thin ceramic green sheets.

In addition to silica and/or calcium carbonate, inactive inorganic particles and/or heat-resistant organic particles can also be used as particles contained in Layer B. However, from the standpoint of transparency and cost, it is more preferable to use silica particles and/or calcium carbonate particles. Other inorganic particles that can be used include alumina-silica composite oxide particles and hydroxyapatite particles. Heat-resistant organic particles include cross-linked polyacrylic particles, cross-linked polystyrene particles, and benzoguanamine particles. When silica particles are used, porous colloidal silica is preferred. When calcium carbonate particles are used, light calcium carbonate that has been surface-treated with a polyacrylic acid-based polymer compound is preferred from the standpoint of preventing the lubricant from falling off.

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 0.3 μm or more and 1.0 μm or less. If the average particle size of the inorganic particles is 0.1 μm or more, the slipperiness of the release film is good, which is preferable. Furthermore, if the average particle size is 2.0 μm or less, there is no risk of adversely affecting the smoothness of the release layer surface, and there is no risk of pinholes occurring in the ceramic green sheet, which is preferable.

In addition, to improve the adhesion of a release layer or the like that will be applied later, or to prevent static electricity, a coating layer may be provided on the surface of surface layer A and/or surface layer B before stretching or after uniaxial stretching during the film-forming process, and corona treatment, etc. may also be performed.

[Release Coating Composition]
The silicone release polyester film of the present invention has a coating layer (release layer) formed using a release coating composition, and the release coating composition comprises 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 Si—H group, a platinum-based catalyst containing a crosslinking reaction inhibitor, and a platinum-based catalyst not containing a crosslinking reaction inhibitor.

The number average molecular weight of the above alkenyl group-containing silicone is 10,000 or more and 40,000 or less.

The total weight of platinum element contained as a platinum-based catalyst is 120 ppm or more and 600 ppm or less relative to the weight of the alkenyl group-containing silicone.

(Alkenyl group-containing silicone)
The alkenyl group-containing silicone used in the present invention is an alkenyl group-containing silicone with a number-average molecular weight of 10,000 to 40,000. This allows for excellent releasability. If the number-average molecular weight of the alkenyl group-containing silicone is below the lower limit, the crosslinking reaction rate increases, resulting in the formation of silicone aggregates. If the number-average molecular weight of the alkenyl group-containing silicone exceeds the upper limit, water dispersion becomes difficult, and the peel strength at the peel speed increases.

The alkenyl group-containing silicone is exemplified by organopolysiloxanes having the structure represented by the following general formula (I):
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 represents an integer of 1 to 3, and b represents an integer of 0 to 2, and a+b≦3.

The alkenyl group-containing silicone may have either a linear or branched structure, may be partially cross-linked, or may be a mixture of these. Examples of alkenyl groups having 2 to 8 carbon atoms represented by ^R1 include vinyl, allyl, butenyl, pentenyl, and hexenyl groups, with vinyl being particularly preferred. Examples of alkyl groups represented by ^R2 include methyl, ethyl, propyl, and butyl groups, and examples of aryl groups include phenyl and tolyl groups. In particular, it is preferred that 80 mol % or more of the substituents on ^R2 be methyl groups in terms of light release properties.

Furthermore, from the viewpoint of the curing speed and pot life of the composition, it is preferable that the proportion of silicon atoms having alkenyl groups be in the range of 0.05 mol % to 20 mol % of the total silicon atoms in the alkenyl group-containing silicone. If the proportion of silicon atoms having alkenyl groups is below the lower limit, the curing speed of the composition will decrease, which may make it difficult to efficiently form a cured silicone coating during the film formation process described below. Furthermore, if the proportion of silicon atoms having alkenyl groups exceeds the upper limit, the pot life of the composition may be shortened.

The alkenyl group-containing silicone of the present invention can be produced by known methods. Furthermore, the alkenyl group-containing silicone of the present invention is contained in the above-mentioned composition in the form of an aqueous dispersion.

(Si—H group-containing silicone)
In the present invention, the silicone having a hydrogen atom directly bonded to a Si atom represented by a Si—H group (hereinafter, sometimes referred to as an Si—H group-containing silicone) is, for example, an organohydrogenpolysiloxane having a structure represented by 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 represents an integer of 0 to 2, and d represents an integer of 1 to 3, and c+d≦3.

The Si—H group-containing silicone may have either a linear or branched chain 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 for 50 mol % or more of the substituents of ^R3 to be methyl groups in terms of light release properties.

From the standpoint of curing characteristics, it is preferable that the above-mentioned Si-H group-containing silicone has at least three hydrogen atoms bonded to silicon atoms, preferably five or more, per silicone molecule.

The above-mentioned Si-H group-containing silicone can be produced by known methods. The Si-H group-containing silicone of the present invention is contained in the above-mentioned composition in the form of an aqueous dispersion.

(Ratio of Number of Si—H Groups to Number of Alkenyl Groups)
The ratio of the number of Si-H groups to the number of alkenyl groups in the release coating composition of the present invention (number of Si-H groups/number of alkenyl groups) is preferably in the range of 1.0 to 2.0. If the above ratio does not reach the lower limit, excess alkenyl groups will remain in the formed coating layer, which may cause the peel strength to easily change over time and may also reduce the crosslink density, resulting in a decrease in the uniformity of the release force and the residual adhesion rate. Furthermore, if the above ratio exceeds the upper limit, highly reactive Si-H groups will remain in the formed coating layer, which may cause an increase in the release force.

(Silicone content)
In the release coating composition of the present invention, the total amount of the alkenyl group-containing silicone solids and the Si—H group-containing silicone solids is preferably 70% by weight or more, based on the solids weight of the composition. The content of each silicone solid is more preferably 80% by weight or more and 97% by weight or less. Here, the silicone solids refers to the amount excluding the aqueous solvent, and the solids weight of the composition refers to the total amount of the solids of each additive. If the total amount of the silicone solids is less than the lower limit, the area covered by the silicone on the film surface on which the coating film is formed will be smaller, resulting in a heavier release force and possibly uneven release force.

(aqueous solvent)
Water is preferably used as the aqueous solvent for forming each of the silicone aqueous dispersions of the present invention. By using an aqueous solvent, it is possible to form a silicone release layer without using explosion-proof equipment and organic solvent recovery equipment, which are required for organic solvents during the process of producing a release film.

(emulsifier)
Each silicone water dispersion is prepared using an emulsifier to increase the stability and shear resistance of the water dispersion. A preferred emulsifier is a nonionic emulsifier, which does not affect the silicone curing reaction. Ionic emulsifiers may affect the silicone curing reaction and may become localized in the coating, e.g., bleed out to the surface, affecting mold releasability.

Nonionic emulsifiers preferably have an HLB value in the range of 8 to 18, and examples include at least one selected from alkylene oxide adducts such as alkylene oxide adducts of higher alcohols or higher fatty acids, esters of alkylene oxide adducts of higher fatty acids and alcohols, alkylene oxide adducts of alkanolamides, alkylene oxide adducts of sorbitan esters, and alkylene oxide adducts of higher fatty acid glycerides. The HLB value is calculated using the Griffin formula.

Examples of alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide. One or more of these may be used. When more than one is used, either block or random addition may be used, but the HLB value is preferably in the range of 8 to 18, and more preferably 10 to 15. Among these nonionic emulsifiers, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, etc. are preferred. Using a nonionic emulsifier with an HLB value outside the above range as an emulsifier for a silicone aqueous dispersion may result in a decrease in emulsifying and dispersing power and the stability of the aqueous dispersion.

(catalyst)
In the release coating composition constituting the coating layer of the present invention, a catalyst is preferably used to cause an addition reaction between the alkenyl group-containing silicone and the Si—H group-containing silicone, and a platinum-based catalyst is particularly preferred. Known platinum-based catalysts can be used, such as platinum chloride and chloroplatinic acid. The platinum-based catalyst may be used in a state where it has been emulsified in advance using a nonionic emulsifier, or it may be used simultaneously with the emulsification of the silicone. Furthermore, a crosslinking reaction inhibitor, which will be described later, may be added during emulsification.

(Crosslinking reaction inhibitor)
In the present invention, a crosslinking reaction inhibitor is contained in the release coating composition to suppress the activity of the platinum-based catalyst at room temperature. The crosslinking reaction inhibitor is preferably a crosslinking reaction inhibitor having an ethynyl group. If the content of the crosslinking reaction inhibitor is too high, the silicone curing reaction is excessively suppressed, making it difficult to form a coating layer (crosslinking reaction). Therefore, the upper limit of the content of the crosslinking reaction inhibitor is not particularly limited as long as it is within a range in which a coating layer is formed taking the above factors into consideration, but it is preferably 6 times or less the amount of platinum element. It is more preferably 5 times or less, and particularly more preferably 4 times or less.

There are no particular limitations on the crosslinking reaction inhibitor having an ethynyl group, as long as it has an ethynyl group. However, since the present invention uses a water-based coating composition, it is preferable to use a crosslinking reaction inhibitor having an ethynyl hydroxyl group, such as 1-ethynylcyclohexanol, in view of the balance between solubility in water and coordination ability to platinum, as well as volatility.

(Platinum-based catalysts with and without crosslinking inhibitors)
In order to efficiently promote the crosslinking reaction, a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor are used in combination.

The mechanism by which the above-mentioned effects of the present invention are realized in the silicone crosslinking reaction in an aqueous dispersion is speculated as follows, but the scope of the present invention is not intended to be limited to this speculation alone. It is speculated that in the silicone crosslinking reaction in an aqueous dispersion, a reaction occurs between polydimethylsiloxane in which the emulsion is broken and a platinum-based catalyst that does not contain a crosslinking reaction inhibitor at low temperatures, and then, at high temperatures, a reaction occurs between polydimethylsiloxane in which the emulsion is completely broken and a platinum-based catalyst that is activated by the volatilization of the crosslinking reaction inhibitor in the platinum-based catalyst that contains a crosslinking reaction inhibitor.

In the present invention, the amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm, relative to the weight of the alkenyl group-containing silicone, and may be, for example, from 130 ppm to 550 ppm, or from 150 ppm to 500 ppm. By keeping the amount within this range, the silicone can be sufficiently cured, resulting in a release film with excellent surface properties that are easy to release.

If the weight ratio of platinum element exceeds the above range, the addition reaction between the alkenyl groups and the Si-H groups will be accelerated, tending to produce a silicone gel. Furthermore, if the weight ratio of platinum element falls below 120 ppm, the addition reaction will proceed, but the silicone will tend to be poorly cured. From the above perspective, it is preferable for the weight ratio to exceed 120 ppm.

The platinum element amount (P1) of the platinum-based catalyst containing the crosslinking reaction inhibitor is preferably 40 ppm or more and less than 400 ppm relative to the weight of the alkenyl group-containing silicone, and may be, for example, 40 ppm or more and 370 ppm or less, or 60 ppm or more and 300 ppm or less.

The amount of platinum element (P0) in the platinum-based catalyst that does not contain the crosslinking reaction inhibitor is preferably 50 ppm or more and less than 400 ppm relative to the weight of the alkenyl group-containing silicone, and may be, for example, 60 ppm or more and 370 ppm or less, or 70 ppm or more and 300 ppm or less.

The platinum-based catalyst contains the platinum element amount (P0) of the platinum-based catalyst that does not contain the crosslinking reaction inhibitor and the platinum element amount (P1) of the platinum-based catalyst that contains the crosslinking reaction inhibitor. The ratio (P0/(P1+P0)) of the platinum element amount (P0) of the platinum-based catalyst that does not contain the crosslinking reaction inhibitor to the total platinum element weight (P1+P0) is preferably 0.3 to 0.8, and may be, for example, 0.31 to 0.75, or may be, for example, 0.32 to 0.70. Since the crosslinking reaction at low temperatures particularly affects the final high crosslink density, if the platinum element weight ratio of the platinum-based catalyst that does not contain the crosslinking reaction inhibitor is less than 0.3, the crosslinking reaction at low temperatures is insufficient, resulting in a film that does not ultimately have a high crosslink density and high peel strength. Furthermore, if the platinum element weight ratio of a platinum-based catalyst that does not contain a crosslinking reaction inhibitor exceeds 0.8, a film with a high crosslink density can be obtained, but since the reaction begins after the coating liquid is prepared, the coating liquid will gel, causing a deterioration in the coating appearance.

(Other ingredients)
To the release coating composition of the present invention, for example, an agent for imparting adhesion to the substrate, a colorant, an ultraviolet absorber, particles, an antistatic agent, etc. may be further added within a range that does not impair the object of the present invention.

(Preparation of silicone water dispersion)
When preparing each of the silicone water dispersions of the present invention, a method of emulsifying the silicone component, aqueous solvent, and emulsifier described above can be used.These components can be emulsified using a known method, such as a method of mechanically emulsifying a pre-prepared silicone and emulsifier, and optionally other components, in an aqueous medium using a stirring device such as a homogenizer, an azihommixer, or an ultraplanetary mixer.

The particle size of the aqueous dispersion can also be adjusted by adjusting the size of the stirring blades, stirring speed, and stirring time. The average particle size of each silicone aqueous dispersion of the present invention is preferably 200 nm or less, and more preferably 100 nm or more and 200 nm or less.

[Coating layer]
In the present invention, a coating layer (release layer) is formed on at least one surface of a polyester film using the release coating composition of the present invention. The coating layer (release layer) of the present invention is formed by applying the release coating composition to the polyester film and then drying the coating composition.

In the present invention, the coating layer thickness, measured after drying, is preferably 5 nm or more and 70 nm or less. If the coating layer thickness is less than the lower limit, the release properties may be insufficient. If the coating layer thickness exceeds the upper limit, the peel strength increases and it becomes difficult to apply the coating liquid because it is necessary to increase its concentration or the amount of coating.

When applying the release coating composition of the present invention to a polyester film, an aqueous coating liquid containing the composition is prepared. The solids concentration of the aqueous coating liquid is preferably 20% by weight or less, based on the weight of the coating liquid, and more preferably 1% by weight or more and 10% by weight or less. If the solids concentration in the aqueous coating liquid is below the lower limit, the coating ability to the polyester film may be insufficient. If the solids concentration exceeds the upper limit, the stability of the coating liquid and the appearance of the coating layer may deteriorate. Water is preferably used as the aqueous solvent for adjusting the solids concentration.

The aqueous coating solution can be applied to the polyester film at any stage, but it is preferable to apply it during the polyester film manufacturing process, and even more preferable to apply it to the polyester film before oriented crystallization is complete.

Here, polyester film before completion of crystal orientation includes unstretched film, uniaxially oriented film obtained by aligning unstretched film in either the machine direction (hereinafter referred to as the continuous film production direction, longitudinal direction, or MD direction) or the cross direction (hereinafter referred to as the direction perpendicular to the machine direction, width direction, or TD direction), and film oriented by low-magnification stretching in both the machine direction and the cross direction (biaxially oriented film before final re-stretching in the machine direction or the cross direction to complete orientation crystallization). Among these, so-called in-line coating is preferred, in which an aqueous coating solution of the composition is applied to an unstretched film or a uniaxially oriented film, followed by machine stretching and/or crosswise stretching and heat setting. The coating layer may be dried by a stretching process or heat setting process after coating, or a further drying process may be added as needed. Furthermore, when the composition is cured using a catalyst to obtain a cured coating, curing can be achieved by a stretching process or heat setting process, but a further curing process may be added as needed.

When applying an aqueous coating liquid to a polyester film, it is preferable to subject the film surface to a physical treatment such as corona surface treatment, flame treatment, or plasma treatment as a preliminary treatment to improve coatability, or to use the aforementioned emulsifier in combination with the composition as a wetting agent.

Any known coating method can be used as the coating method. For example, roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, curtain coating, etc. can be used alone or in combination.

<Method of manufacturing silicone release polyester film>
The method for producing a silicone release polyester film of the present invention comprises the steps of:
A method for producing a silicone release polyester film, comprising the steps of: forming a coating layer on at least one surface of a polyester film using a release coating composition comprising 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 Si—H group, and an aqueous dispersion containing a platinum-based catalyst;
The amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm relative to the weight of the alkenyl group-containing silicone,
The platinum-based catalyst includes a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor,
The thickness of the coating layer is 5 nm or more and 70 nm or less.

The method for producing a silicone release polyester film of the present invention makes it possible to efficiently and easily obtain a silicone release polyester film having the above-mentioned properties. Note that the production method shown here is only an example, and the present invention is not limited to this.

In the above manufacturing method, the descriptions in this specification regarding the above silicone release polyester film, etc. can be applied mutatis mutandis to each component, as appropriate.

In the above manufacturing method, any known method can be used as the step of forming a coating layer using a water-dispersed release coating composition, as long as it is a method of forming a coating layer on a film using a water-dispersed release coating composition.

<Protected object>
In the object to be protected of the present invention, the silicone release polyester film is laminated on the surface of the coating layer or the surface of the release layer.

Examples of the object to be protected include organic resin sheets, inorganic resin sheets, glass plates, metal plates, ceramic sheets, and adhesive sheets. Because the object to be protected of the present invention is laminated with a silicone release polyester film having the above-described properties, it can be suitably used when the object to be protected is, for example, a ceramic green sheet.

The present invention will be explained in detail using examples, but the present invention is not limited to the following examples. The physical properties and characteristics in the examples were measured or evaluated using the methods described below. Furthermore, the term "parts" means "parts by mass."

The measurements and evaluations in the examples were carried out as follows:

(1) Ceramic sheet releasability 90 parts by weight of barium titanate (BaTiO ₃ ), 7 parts by weight of polyvinyl butyral, 1.5 parts by weight of dioctyl phthalate, and 2.5 parts by weight of a polycarboxylic acid-based polymer surfactant were added to a mixed solvent of toluene:ethanol = 1:1 (volume ratio), and dispersed using a ball mill to prepare a slurry. This slurry was uniformly coated on the coating layer (release layer) of a release polyester film so that the thickness after drying would be 2 μm, and then dried to form a ceramic sheet.

The release polyester film on which the ceramic sheet was formed was cut to a size of 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 specimen. This test specimen was conditioned at 23°C and 50% humidity for 24 hours, and then the ceramic sheet (31B tape side) was peeled off using a tensile tester at a peel angle of 90° and a peel speed of 10 m/min, and the peel strength was measured.

The peel strength of the ceramic sheets was judged based on the following index.
○: Peel strength is 0.60 g/25 mm or less ×: Peel strength is more than 0.60 g/25 mm

(2) Residual Adhesion Rate A polyester adhesive tape (manufactured by Nitto Denko, No. 31B) was attached to a cold-rolled stainless steel plate (SUS304) as specified in JIS G4305, and the peel strength was measured and recorded as the basic adhesive strength (f0). The polyester adhesive tape was also pressed onto the release layer surface of a release polyester film with a 5 kg pressure roller, maintained for 30 seconds, and then peeled off. The peeled adhesive tape was then attached to the stainless steel plate, and the peel strength was measured and recorded as the residual adhesive strength (f). The residual adhesion rate was calculated from the obtained basic adhesive strength (f0) and residual adhesive strength (f) using the following formula. The peel angle was 180 degrees and the peel speed was 300 mm/min.
Residual adhesion rate (%) = (f) / (f0) x 100
A residual adhesion rate of 90% or more is preferable, indicating a high silicone crosslink density, and a rate of less than 90% indicates insufficient crosslinking.

(3) Coating Layer Thickness The film was fixed with an embedding resin, and its cross section was cut with a microtome so that the film cross section could be observed. The film was stained with 2% osmic acid at 60°C for 2 hours, and observed using a transmission electron microscope (JEM2010 manufactured by JEOL Ltd.) to measure the thickness of the release layer.

(4) Coating Uniformity The coating uniformity of the release layer was evaluated by visually observing the surface of the release layer under reflected light and by the following criteria.
⊚: No coating defects, very uniform coating.
◯: No coating defects, but slight rainbow-patterned spots observed in the longitudinal direction.
Δ: Slightly fine coating defects and coating streaks in the longitudinal direction are observed.
x: Many fine coating defects occurred, and strong coating streaks were observed in the longitudinal direction, making it impossible to say that the coating was uniform.

[Examples 1 to 5, Comparative Examples 1 to 8]
Molten polyethylene terephthalate ([η]=0.64 dl/g, Tg=78°C) containing 0.1% by mass of calcium carbonate particles having an average particle size of 0.7 µm was extruded through a die and cooled on a cooling drum in a conventional manner to form an unstretched film. The film was then stretched 3.6 times in the longitudinal direction, and an aqueous coating liquid (aqueous dispersion with a solids concentration of 5% by mass) prepared by mixing the components to obtain the solids content ratio shown in Table 1 was uniformly applied to the surface of the film using a roll coater to form a coating layer (release layer) so that the coating thickness after drying would be 30 nm.

The coated film was then dried at 115°C for approximately 5 seconds, stretched 4.5 times in the transverse direction at 145°C, and further heat-set at 230°C for approximately 5 seconds to obtain a 25 μm biaxially oriented polyester film having the coating layer (release layer) shown in Table 1.

<Alkenyl Group-Containing Silicone Water Dispersion>
Using an emulsifying device capable of stirring the entire container (manufactured by N.P. Labo Co., Ltd., device name "Ultra Planetary Mixer"), raw materials consisting of 98% by weight of silicone (number average molecular weight: 28,000) having an alkenyl group represented by the following formula (1) and 2% by weight of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain an alkenyl group-containing silicone aqueous dispersion with a solid content of 20% by weight. Furthermore, the emulsion particle size was adjusted by adjusting the stirring speed and stirring time during emulsification.

(In formula (1), m is 2, and n was adjusted so that the number average molecular weight was 28,000.)

<Si—H Group-Containing Silicone Water Dispersion>
Using an emulsifier capable of stirring the entire contents of a container (manufactured by N.P. Labo, device name "Ultra Planetary Mixer"), raw materials consisting of 98% by weight of silicone (number average molecular weight: 5000) having hydrogen groups represented by formula (2) below and 2% by weight of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade name "Emulgen 109P") as a surfactant were mechanically emulsified in an aqueous medium to obtain an Si—H group-containing silicone aqueous dispersion with a solids content of 20% by weight. The emulsion particle size was also adjusted by adjusting the stirring speed and stirring time during emulsification.

(In formula (2), o = 40 and p = 35.)

<Platinum-based catalyst>
Platinum catalyst containing reaction inhibitor (P1): An aqueous dispersion of 10% by weight of solids was prepared using an isopropyl alcohol solution of chloroplatinic acid (in an amount such that the platinum metal in the composition was 500 ppm by mass), 99.75% by weight of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade name "Emulgen 109P") as a surfactant, 0.2% by weight of a crosslinking reaction inhibitor (1-ethynylcyclohexanol), and pure water. Because the crosslinking reaction inhibitor is preferentially coordinated to the platinum catalyst (P1), the catalytic effect can be delayed until the reaction inhibitor volatilizes.

Platinum-based catalyst (P0) without reaction inhibitor: An aqueous dispersion was prepared using an isopropyl alcohol solution of chloroplatinic acid (an amount that results in 500 ppm platinum metal by mass in this composition), 99.95% by weight of polyoxyethylene lauryl ether (Kao Corporation, product name "Emulgen 109P") as a surfactant, and pure water. Because the platinum-based catalyst (P0) does not contain a reaction inhibitor, it is able to demonstrate catalytic activity even at low temperatures.

<Preparation of silicone coating solution>
A release coating composition was prepared by using a composition consisting of 90 parts by weight of an alkenyl group-containing silicone aqueous dispersion/10 parts by weight of an Si—H group-containing silicone aqueous dispersion/platinum-based catalyst (the amount added was adjusted so that the platinum element amount of P0+P1 was as shown in Table 1), and diluting it with water to a solids concentration of 5% in the coating liquid so as to achieve the target coating layer thickness.

The above formulation and results are shown in Table 1.

As can be seen from Table 1, the films of the examples of the present invention exhibited excellent peelability, residual adhesion, and appearance. This was due to the combination of a catalyst containing a crosslinking inhibitor with a catalyst not containing one, resulting in a film with extremely high crosslink density. On the other hand, in Comparative Examples 1 and 2, the total amount of platinum element was too high, resulting in gelation and poor coating appearance. In Comparative Examples 3 and 4, the total amount of platinum element was too low, resulting in poor results. In Comparative Example 5, the crosslinking reaction proceeded excessively from the low temperature range, reducing the amount of available platinum element in the high temperature range, ultimately resulting in reduced crosslink density and increased peel strength. In Comparative Example 6, the effective amount of platinum element in the low temperature range decreased, preventing crosslinking reaction from proceeding at low temperatures and remaining limited to the high temperature range, resulting in reduced crosslink density and increased peel strength. In Comparative Example 7, the total amount of platinum element was too high, resulting in excessive crosslinking reaction from the low temperature range, resulting in poor coating appearance. In Comparative Example 8, the total amount of platinum element was too high, resulting in excessive crosslinking reaction only in the high temperature range, resulting in poor coating appearance.

Claims (14)

A silicone release polyester film having a coating layer formed on at least one surface of the polyester film using a release coating composition comprising 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 an Si—H group, and an aqueous dispersion containing a platinum-based catalyst,
the amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm relative to the weight of the alkenyl group-containing silicone;
The platinum-based catalyst includes a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor,
The thickness of the coating layer is 5 nm or more and 70 nm or less,
the platinum-based catalyst contains a platinum element amount (P0) of a platinum-based catalyst that does not contain the crosslinking reaction inhibitor, and a platinum element amount (P1) of a platinum-based catalyst that contains the crosslinking reaction inhibitor,
a ratio (P0/(P1+P0)) of the amount of platinum element (P0) in the platinum-based catalyst not containing a crosslinking reaction inhibitor to the total weight of platinum element (P1+P0) is 0.3 or more and 0.8 or less,
the ratio of the number of Si—H groups to the number of alkenyl groups (number of Si—H groups/number of alkenyl groups) is 1.0 or more and 2.0 or less;
Silicone release polyester film. the platinum element amount (P0) of the platinum-based catalyst not containing a crosslinking reaction inhibitor is 50 ppm or more and less than 400 ppm relative to the weight of the alkenyl group-containing silicone,
the platinum element amount (P1) of the platinum-based catalyst containing the crosslinking reaction inhibitor is 40 ppm or more and less than 400 ppm relative to the weight of the alkenyl group-containing silicone;
The silicone release polyester film according to claim 1 . 2. The silicone release polyester film according to claim 1, wherein the alkenyl group-containing silicone has a number average molecular weight of 10,000 or more and 40,000 or less. 2. The silicone release polyester film according to claim 1 , wherein the alkenyl group of the alkenyl group-containing silicone is a vinyl group. 2. The silicone release polyester film according to claim 1, wherein the ratio of silicon atoms having an alkenyl group to all silicon atoms in the alkenyl group-containing silicone is from 0.05 mol % to 20 mol %. 2. The silicone release polyester film according to claim 1, wherein the ratio (P0/(P1+P0)) of the amount of platinum element (P0) in the platinum-based catalyst not containing the crosslinking reaction inhibitor to the total weight of platinum element (P1+P0) is 0.32 or more and 0.70 or less. 2. The silicone release polyester film according to claim 1, wherein the residual adhesion rate of the silicone release polyester film is 90% or more. 2. The silicone release polyester film according to claim 1 , which is used in forming ceramic green sheets in the production of multilayer ceramic capacitors. 9. The object to be protected, wherein the silicone release polyester film according to claim 1 is laminated on the surface of the coating layer or the surface of the release layer. The object to be protected according to claim 9 , wherein the object to be protected is a ceramic green sheet. A method for producing a silicone release polyester film, comprising the steps of: forming a coating layer on at least one surface of a polyester film using a release coating composition comprising 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 Si—H group, and an aqueous dispersion containing a platinum-based catalyst;
the amount of platinum element in the platinum-based catalyst is more than 120 ppm and less than 600 ppm relative to the weight of the alkenyl group-containing silicone;
The platinum-based catalyst includes a platinum-based catalyst containing a crosslinking reaction inhibitor and a platinum-based catalyst not containing a crosslinking reaction inhibitor,
The thickness of the coating layer is 5 nm or more and 70 nm or less,
the platinum-based catalyst contains a platinum element amount (P0) of a platinum-based catalyst that does not contain the crosslinking reaction inhibitor, and a platinum element amount (P1) of a platinum-based catalyst that contains the crosslinking reaction inhibitor,
a ratio (P0/(P1+P0)) of the amount of platinum element (P0) in the platinum-based catalyst not containing a crosslinking reaction inhibitor to the total weight of platinum element (P1+P0) is 0.3 or more and 0.8 or less,
the ratio of the number of Si—H groups to the number of alkenyl groups (number of Si—H groups/number of alkenyl groups) is 1.0 or more and 2.0 or less;
Method for producing silicone release polyester film. The method for producing a silicone release polyester film according to claim 11, wherein the step of forming the coating layer is carried out by in-line coating on an unstretched film or a uniaxially stretched film that has been oriented in one direction. The method according to claim 11, wherein the aqueous coating liquid used in the step of forming the coating layer has a solids concentration of 1% by weight or more and 10% by weight or less. The method according to claim 12 , wherein after the step of forming the coating layer, the coating layer is dried and cured by a stretching step and/or a heat setting treatment.