JP7513065B2 - Release Film - Google Patents

Description

The present invention relates to a release film having a release layer containing a silicone compound on at least one side of a polyester film.

One example of a method for manufacturing liquid crystal display devices used as image display devices in liquid crystal televisions, computer displays, mobile phones, digital cameras, etc. is to attach a release film to one side of an adhesive layer, and then attach the adhesive layer to a polarizing plate to produce an adhesive layer-attached polarizing plate. When attaching the plate to a liquid crystal cell, the release film is peeled off and the adhesive layer and the glass substrate of the liquid crystal cell are attached to produce the plate.

In recent years, with the increase in size of displays, the dimensions of optical components such as polarizing plates and release films have also increased, and the release films used in the manufacture of liquid crystal display devices as described above are now required to have the property of being able to be easily peeled off even when the peel area is large, that is, to be able to be peeled off with a small force (also referred to as "light peelability").
In this respect, silicone is a material that has excellent properties that allow it to be peeled off with a small force due to the flexibility of the siloxane skeleton and the low surface energy due to methyl group substitution. Therefore, release films with a release layer containing silicone have been attracting attention as release films for protecting adhesives that bond optical members, such as members that constitute liquid crystal displays.

Patent Document 1 discloses a silicone release polyester film having a coating layer formed using a release coating composition that contains an aqueous dispersion of an alkenyl group-containing silicone, an aqueous dispersion of a silicone having a Si-H group, and a crosslinking reaction inhibitor having an ethynyl group.

Patent Document 2 discloses a silicone release film having a coating layer formed on at least one side of a base film using a release coating composition that includes an aqueous dispersion of an alkenyl group-containing silicone, an aqueous dispersion of a silicone having a Si-H group, and an aqueous dispersion of an acrylic resin that is substantially free of carboxyl groups and ionic groups in its main skeleton and side chains.

JP 2013-208810 A JP 2014-213590 A

As described above, it was found that the release performance of a release film having a structure in which a release layer containing a silicone compound is laminated on a polyester film (substrate) tends to decrease when the release layer comes into contact with a solvent. For example, when a solvent-containing adhesive resin composition is applied to a release layer to form an adhesive layer on the release layer, the release performance of the release layer decreases, and the adhesive layer may become difficult to peel off. In particular, this tendency is more pronounced when the release layer comes into contact with a solvent after the release film is stored for a long period of time with the release layer laminated on the polyester film (substrate). This is thought to be due to a decrease in adhesion between the release layer and the polyester film (substrate).

The present invention aims to provide a new release film and a method for producing the same, which has a release layer containing a silicone compound on at least one side of a polyester film (substrate), and which can maintain adhesion between the polyester film (substrate) and the release layer and can maintain excellent releasability even when the release layer comes into contact with a solvent.

The present invention proposes a release film having a release layer on at least one side of a polyester film, the release layer containing a silicone compound and a compound containing a (meth)acryloyl group.

The present invention also proposes a release film having a release layer on at least one side of a polyester film, the release layer being formed from a release layer-forming composition that contains a silicone compound and a compound that contains a (meth)acryloyl group.

The present invention also proposes a method for producing a release film, which is characterized by forming a release layer by applying a release layer-forming composition containing a silicone compound and a compound containing a (meth)acryloyl group to at least one side of a polyester film.

The release film proposed by the present invention can maintain the adhesion between the polyester film (substrate) and the release layer even when the release layer contacts with a solvent by including a compound containing a (meth)acryloyl group in addition to a silicone compound in the release layer laminated on the polyester film (substrate). Therefore, for example, when forming a pressure-sensitive adhesive sheet with a release layer, a pressure-sensitive adhesive resin composition containing a solvent is applied onto the release layer, and the adhesion between the polyester film (substrate) and the release layer can be maintained even when the release layer contacts with a solvent.
Moreover, according to the method for producing a release film proposed by the present invention, the above release film proposed by the present invention can be produced.

Next, the present invention will be described based on an embodiment example. However, the present invention is not limited to the embodiment described below.

＜＜Release film＞＞
A release film according to one embodiment of the present invention (referred to as "this release film") is a release film having a release layer (referred to as "this release layer") on one or both sides of a polyester film (referred to as "this polyester film") as a substrate, and the release layer is characterized by containing a silicone compound and a compound containing a (meth)acryloyl group.

<This polyester film>
The polyester film serves as the substrate for the release film.
The polyester film may be a non-stretched film (sheet) or a stretched film. Of these, a uniaxially or biaxially stretched film is preferred. Of these, a biaxially stretched film is preferred in terms of excellent balance of mechanical properties and flatness.

(Genuine polyester)
The polyester that is the main component resin of the present polyester film (also referred to as "the present polyester") may be either a homopolyester or a copolymer polyester.

The above-mentioned main component resin means the resin that has the largest mass ratio among the resins that make up the polyester film, and can be 50 mass% or more, 75 mass% or more, 90 mass% or more, or 100 mass% of the resins that make up the polyester film.

When the present polyester is a homopolyester, it is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol.
Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol.
Representative examples of polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

On the other hand, when the present polyester is a copolymer polyester, it is preferable that the copolymer contains 30 mol % or less of a third component.
Examples of the dicarboxylic acid component of the copolymer polyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid, and the like, which may be used alone or in combination.
Examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

The polyester is preferably composed of polyethylene terephthalate, which is usually 80 mol % or more, and preferably 90 mol % or more, of ethylene terephthalate units, or polyethylene-2,6-naphthalate, which is ethylene-2,6-naphthalate units.

(particle)
The polyester film may contain particles for the main purpose of imparting lubricity.
The type of particles is not particularly limited as long as they are particles capable of imparting lubricity. Examples of the particles include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide. Heat-resistant organic particles described in JP-B-59-5216 and JP-A-59-217755 may also be used. Other examples of heat-resistant organic particles include thermosetting urea resins, thermosetting phenolic resins, thermosetting epoxy resins, and benzoguanamine resins. Furthermore, precipitated particles obtained by precipitating a part of a metal compound such as a catalyst during the polyester production process may also be used.
The shape of the particles is not particularly limited, and may be, for example, any of spherical, blocky, rod-like, flat, and the like.
There are no particular limitations on the hardness, specific gravity, color, etc. of the particles.
Furthermore, two or more types of particles may be used in combination, if necessary.

The average particle size of the particles is preferably 0.1 to 5 μm.
If the average particle size of the particles is 0.1 μm or more, the aggregation of the particles can be suppressed and dispersibility can be ensured, whereas if the average particle size of the particles is 5 μm or less, the surface roughness of the film is not too high, and a release layer can be suitably provided in a later step.
From this viewpoint, the average particle size of the particles is preferably 0.1 to 5 μm, and more preferably 0.5 μm or more or 3 μm or less.

The particle content in the present polyester film is preferably from 0.0003 to 5% by mass.
If the particle content is 0.0003% by mass or more, the film can have a favorable slipperiness, whereas if the particle content is 5% by mass or less, the film surface can have a sufficiently smooth surface.
From this viewpoint, the particle content is preferably 0.0003 to 5% by mass, and more preferably 0.001 to 3% by mass.

(Other Additives)
The polyester film may further contain other additives, such as antioxidants, heat stabilizers, lubricants, dyes, pigments, etc., if necessary.

(Thickness of this polyester film)
The thickness of the polyester film is preferably as thin as possible from the viewpoint of cost. On the other hand, if the thickness is too thin, not only may the flatness of the film be impaired due to wrinkles caused by heat treatment during processing, but the protective function as a release film may also be insufficient. Therefore, the thickness of the polyester film is preferably 10 μm to 125 μm, and more preferably 12 μm or more or 75 μm or less.

The polyester film of the present invention may be a single-layer film or a multi-layer film having two or more layers, and is not particularly limited.
When particles are incorporated into the present polyester film, from the viewpoint of ensuring transparency without reducing slipperiness, a three-layer structure is preferable, and from the viewpoint of ease of production, a three-layer structure is more preferable, and a structure in which particles are incorporated into the outermost layer is optimal.

<Release layer>
The release layer is a layer containing a silicone compound and a compound containing a (meth)acryloyl group.
Here, the silicone compound and the compound containing a (meth)acryloyl group are used as different compounds, i.e., it does not mean that only the silicone compound containing a (meth)acryloyl group is used.

When a release layer containing a silicone compound, for example a release layer formed by crosslinking or curing a silicone compound, comes into contact with a solvent such as toluene, the insufficiently cured uncured parts dissolve or swell, and the adhesion between the base film, which is a polyester film, and the release layer tends to decrease. This tendency is particularly pronounced when the release layer comes into contact with a solvent such as toluene after being stored for a long period of time in a state in which the release layer is laminated on a polyester film.
In response to this, the present inventor, through various investigations, has found that when the present release layer is formed by combining a silicone compound with a compound containing a (meth)acryloyl group, even if the present release layer comes into contact with a solvent, the adhesiveness between the polyester film (substrate) and the release layer can be maintained. Although the reason for this is unclear, it is believed that the compound containing a (meth)acryloyl group affects the adhesiveness between the silicone compound and the polyester film.

The release layer preferably has a crosslinked structure having a skeleton derived from a silicone compound, which is preferable because the release layer can ensure release performance.
Among these, it is preferable to have a crosslinked structure having a skeleton derived from a silicone compound and a compound containing a (meth)acryloyl group, since it is considered that the adhesion between the polyester film and the release layer is improved if the crosslinked structure is present.
Among these, those containing a Si-H group derived from a silicone compound and/or a urethane structure derived from a urethane (meth)acrylate are more preferred from the viewpoint of adhesion between the polyester film and the release layer.

(Silicone Compound)
A silicone compound is a compound having a silicone structure in the molecule, in other words, a compound having a main skeleton formed by siloxane bonds.
Examples of silicone compounds or main skeletons constituting silicone compounds include organopolysiloxanes such as polydimethylsiloxane, acrylic grafted silicone, silicone grafted acrylic, amino-modified silicone, perfluoroalkyl-modified silicone, alkyl-modified silicone, etc. Among these, organopolysiloxanes such as polydimethylsiloxane are preferred from the viewpoint of excellent releasability.

Among these, silicone compounds having a functional group capable of reacting with a (meth)acryloyl group are preferred, and among these, silicone compounds containing a Si-H group are particularly preferred.
The Si-H group of the silicone compound has the property of increasing adhesion to the polyester film. However, the Si-H group may decrease due to aging, for example, when the release film is stored for a long period of time, and the adhesion to the polyester film may decrease. Therefore, by blending a compound containing a (meth)acryloyl group, the adhesion to the polyester film can be further increased.
Among these, silicone compounds having a Si-H group and an alkenyl group are preferred from the viewpoint of forming a crosslinked structure having a skeleton derived from the silicone compound in the present release layer.

The molecular weight of the silicone compound is not particularly limited. In particular, from the viewpoint of adhesion between the polyester film (substrate) and the release layer, the number average molecular weight is preferably 5000 or more, more preferably 10000 or more. The upper limit is not particularly limited, but is usually 1,000,000 or less.
The number average molecular weight of the silicone compound can be measured, for example, by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.

The silicone compound is preferably contained in the release layer in an amount of 50 to 99% by weight.
If the silicone compound is contained in the release layer in an amount of 50% by mass or more, sufficient releasability is obtained, which is preferable, and if it is contained in an amount of 99% by mass or less, sufficient solvent resistance is obtained, which is preferable.
From this viewpoint, it is preferable that the silicone compound is contained in the release layer in an amount of 50 to 99% by mass, more preferably 60% by mass or more or 99% by mass or less, and even more preferably 70% by mass or more or 98% by mass or less.

(Compound containing a (meth)acryloyl group)
The compound containing a (meth)acryloyl group may be either a polymeric (meth)acrylate compound or a monomeric (meth)acrylate compound, or they may be used in combination.
Here, the polymeric (meth)acrylate compound means a macromonomer.

Examples of the (meth)acrylate compound include urethane (meth)acrylate compounds, epoxy (meth)acrylate compounds, polyester (meth)acrylate compounds, polyalkylene (meth)acrylate compounds, and other (meth)acrylate compounds.
In this specification, the terms "a compound containing a (meth)acryloyl group", "a (meth)acrylate compound", and "a (meth)acrylate" all refer to a concept that encompasses both a compound containing an acryloyl group and a compound having a methacryloyl group, and may contain either an acryloyl group, a methacryloyl group, or both.

The urethane (meth)acrylate compound may be any known compound, and is not particularly limited. Examples of such compounds include compounds obtained by reacting a (meth)acrylate compound having a hydroxyl group with an isocyanate compound, and compounds obtained by reacting a (meth)acrylate compound having a hydroxyl group with a polyol and an isocyanate compound. The urethane (meth)acrylate compound may be a polymer or a monomer, but is preferably a polymer from the viewpoint of adhesion to the polyester film.

Examples of (meth)acrylate compounds having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate, diglycerin mono(meth)acrylate, diglycerin tri(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol mono(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, sorbitol di(meth)acrylate, sorbitol tri(meth)acrylate, sorbitol tetra(meth)acrylate, sorbitol penta(meth)acrylate, Examples of the reaction products include reaction products of (meth)acrylic acid and polyol diglycidyl such as (meth)acrylic acid, sorbitol mono(meth)acrylate diglycerin di(meth)acrylate, an adduct of glycidyl (meth)acrylate and (meth)acrylic acid, a reaction product of two molecules of (meth)acrylic acid and one molecule of 1,6-hexanediol diglycidyl, a reaction product of two molecules of epoxy (meth)acrylic acid and one molecule of neopentyl glycol diglycidyl, a reaction product of two molecules of (meth)acrylic acid and one molecule of bisphenol A diglycidyl, a reaction product of two molecules of (meth)acrylic acid and a diglycidyl form of a propylene oxide adduct of bisphenol A, a reaction product of two molecules of (meth)acrylic acid and one molecule of diglycidyl phthalate, a reaction product of two molecules of (meth)acrylic acid and one molecule of polyethylene glycol diglycidyl, and a reaction product of two molecules of (meth)acrylic acid and one molecule of polypropylene glycol diglycidyl. These may be used alone or in combination with multiple types.

Among these, from the viewpoint of more effectively improving the adhesion between the silicone compound and the polyester film, those having three or more (meth)acryloyl groups in one molecule, such as diglycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, sorbitol tri(meth)acrylate, sorbitol tetra(meth)acrylate, and sorbitol penta(meth)acrylate, are preferred, and those having five or more (meth)acryloyl groups in one molecule, such as dipentaerythritol penta(meth)acrylate and sorbitol penta(meth)acrylate, are more preferred.

An isocyanate compound is a compound that has an isocyanate or an isocyanate derivative structure, such as a blocked isocyanate. Examples of the isocyanate include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, ethylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, methylene bis(4-cyclohexyl isocyanate), and isopropylidenedicyclohexyl diisocyanate. The isocyanates may be reaction products of various polymers or compounds. Examples of polymers or derivatives of the isocyanates include biuretized products, isocyanurates, uretdione products, and carbodiimide modified products. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are preferred, and alicyclic isocyanates are more preferred, from the viewpoint of improving the adhesion of the release layer to the polyester film.

Examples of polyols include polycarbonate polyols, polyester polyols, polyether polyols, etc., and high molecular weight polyols and low molecular weight polyols can be used.

There are no particular limitations on the high molecular weight polyol, but it is preferable that the number average molecular weight is 400 to 8,000, and more preferably 400 to 4,000. If the number average molecular weight is in this range, it will have an appropriate viscosity and will be possible to obtain a good appearance of the release layer.

Examples of high molecular weight polyols include polycarbonate polyols, polyester polyols, polyether polyols, etc. Polycarbonate polyols are preferred to improve adhesion to polyester films.

Polycarbonate polyols are obtained by dealcoholization reaction between polyhydric alcohols and carbonate compounds. Examples of polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylolheptane 1,4-benzenedimethanol, 1,3-benzenedimethanol, 4,4'-naphthalenedimethanol, and 3,4'-naphthalenedimethanol. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate, and examples of polycarbonate polyols obtained by the reaction of these compounds include polyhexamethylene carbonate diol and polycyclohexylene carbonate diol. Among these, polyhexamethylene carbonate diol is preferred from the viewpoint of adhesion of the release layer to the polyester film.

Examples of polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-methyl-2,4-pentanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5 ...2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl 2-ethyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamine, lactonediol, etc.), and those having derivative units of lactone compounds such as polycaprolactone.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, etc.

The low molecular weight polyol is not particularly limited, but examples thereof include those having a number average molecular weight of 60 or more and less than 400. For example, aliphatic diols having 2 to 9 carbon atoms such as ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol; 1,4-cyclohexanediol; Examples of the diols having an alicyclic structure with 6 to 12 carbon atoms, such as ethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanediol, 1,4-bis(hydroxyethyl)cyclohexane, 2,7-norbornanediol, tetrahydrofuran dimethanol, and 2,5-bis(hydroxymethyl)-1,4-dioxane, as well as dimethylolalkanoic acids, such as 2,2-dimethylolpropanoic acid and 2,2-dimethylolbutanoic acid, and low molecular weight polyhydric alcohols, such as trimethylolpropane, pentaerythritol, and sorbitol. Among these, dimethylolalkanoic acids are preferred from the viewpoint of improving the stability of the aqueous dispersion of the urethane (meth)acrylate compound.

The epoxy (meth)acrylate compound may be any conventionally known compound, and is not particularly limited. For example, it may be a compound obtained by reacting an epoxy resin with (meth)acrylic acid or a carboxyl group-containing (meth)acrylate.

Epoxy resins include compounds containing epoxy groups in the molecule, such as condensates of epichlorohydrin with hydroxyl groups or amino groups of ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc., polyepoxy compounds such as polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether, novolac-type epoxy resins of cresol novolac type and phenol novolac type, and bisphenol-type epoxy resins such as bisphenol A type, bisphenol F type, and bisphenol S type. Among these, cresol novolac-type epoxy resins are preferred.

(Meth)acrylic acids include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, citraconic acid, etc.

The epoxy (meth)acrylate compound is preferably a composite resin composed of a urethane resin, from the viewpoint of further improving the adhesion to the polyester film.
As the urethane resin, a conventionally known urethane resin can be used.
Generally, urethane resins are produced by reacting polyols with isocyanates.
Examples of the polyol include the above-mentioned polyester polyol, polycarbonate polyol, polyether polyol, etc., and these compounds may be used alone or in combination of two or more kinds.
Of the above, polyester polyols are more preferred in terms of adhesion to polyester films.

Examples of the (meth)acrylate compound include monofunctional (meth)acrylates, bifunctional (meth)acrylates, polyfunctional (meth)acrylates, etc. Here, the polyfunctional (meth)acrylate refers to a compound having three or more (meth)acrylate groups in one molecule.
The (meth)acrylate compound may be a polymer or a monomer, and is preferably a monomer from the viewpoint of reactivity with the silicone compound.

The monofunctional (meth)acrylate is not particularly limited. For example, alkyl (meth)acrylates such as methyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate, hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, and ethoxypropyl (meth)acrylate, etc. Examples of such acrylates include aromatic (meth)acrylates such as alkoxyalkyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate; amino group-containing (meth)acrylates such as diaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; ethylene oxide-modified (meth)acrylates such as methoxyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and phenylphenol ethylene oxide-modified (meth)acrylate; glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and (meth)acrylic acid.

Examples of bifunctional (meth)acrylates include, but are not limited to, alkanediol di(meth)acrylates such as 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, bisphenol-modified di(meth)acrylates such as bisphenol A ethylene oxide-modified di(meth)acrylate and bisphenol F ethylene oxide-modified di(meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, urethane di(meth)acrylate, and epoxy di(meth)acrylate.

The polyfunctional (meth)acrylate is not particularly limited, but examples thereof include alkylenoxide-modified trimethylolpropane tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, and propylene oxide-modified trimethylolpropane tri(meth)acrylate, isocyanuric acid-modified tri(meth)acrylates such as ethylene oxide-modified isocyanuric acid tri(meth)acrylate, and ε-caprolactone-modified tris(acryloxyethyl)isocyanurate, pentaerythritol tri(meth)acrylate, and the like. Examples of such alkylene oxide-modified pentaerythritol tetra(meth)acrylates include ethylene oxide-modified pentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, tetramethylolmethane ethylene oxide-modified tetra(meth)acrylate, ethylene oxide-modified pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

Among these, from the viewpoint of more efficiently forming crosslinks and increasing the solvent resistance of the release layer, bifunctional (meth)acrylates or polyfunctional (meth)acrylates are preferred, and polyfunctional (meth)acrylates are more preferred. Specifically, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate are preferred, and trimethylolpropane tri(meth)acrylate and dipentaerythritol hexa(tri)acrylate are more preferred.

The compound containing a (meth)acryloyl group is preferably a urethane (meth)acrylate, or a mixture of a urethane (meth)acrylate and a (meth)acrylate compound other than a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin.
It has been known that when a silicone compound is crosslinked or cured to form a release layer, if the silicone compound is combined with a urethane resin, the urethane resin inhibits the curing of the silicone compound. Therefore, it has been common technical knowledge to avoid combining a urethane-based compound with a silicone compound. However, surprisingly, as described above, when a urethane (meth)acrylate, or a urethane (meth)acrylate and a (meth)acrylate compound other than a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin are combined and blended as a compound containing a (meth)acryloyl group in the release layer, it has been confirmed that even if the release layer comes into contact with a solvent, the adhesion between the polyester film (substrate) and the release layer can be effectively suppressed from decreasing.

In this way, when a combination of a urethane (meth)acrylate, or a (meth)acrylate compound other than a urethane (meth)acrylate and a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin is used as a compound containing a (meth)acryloyl group, it is preferable that the release layer has a crosslinked structure including a Si-H group and a urethane structure, as described above.
In this case, the Si-H group is derived from the silicone compound, and the urethane structure is derived from the urethane (meth)acrylate.
Generally, silicone compounds are hydrophobic and have low surface free energy. On the other hand, polyurethane resin skeletons are highly polar and have high surface free energy. Therefore, even if these are mixed, it is believed that they will usually repel each other and form a separated structure. However, in the present invention, it has been found that if the urethane structure is introduced as urethane (meth)acrylate instead of polyurethane, some of the (meth)acryloyl groups react with the silicone compound, thereby suppressing the separation of the two. It is believed that this has led to the introduction of the urethane structure, which is an improvement over the insufficient solvent resistance of silicone compounds alone.
This technical idea is not limited to urethane (meth)acrylates, but may also be applied to other compounds containing a (meth)acryloyl group. Furthermore, the present invention is not limited to cases where the above technical idea is clearly expressed.

(Other ingredients)
The release layer can contain other components in addition to the silicone compound and the compound containing a (meth)acryloyl group. For example, it is also possible to use polymers, crosslinking agents, particles, defoamers, coating improvers, thickeners, organic lubricants, antistatic agents, UV absorbers, antioxidants, foaming agents, dyes, pigments, etc. in combination. Specific examples of polymers include polyester resins, acrylic resins, urethane resins, polyvinyls (polyvinyl alcohol, vinyl chloride-vinyl acetate copolymers, etc.), polyalkylene glycols, polyalkyleneimines, methylcellulose, hydroxycellulose, starches, etc.

The components contained in this release layer can be analyzed using, for example, TOF-SIMS, X-ray photoelectron spectroscopy (ESCA), X-ray fluorescence, etc.

(Thickness of this release layer)
The thickness of the release layer is preferably 0.005 μm to 1 μm.
If the thickness of this release layer is 1 μm or less, deterioration of the coating appearance and insufficient curing of the coating can be prevented, and if the thickness of this release layer is 0.005 μm or more, sufficient releasability can be obtained.
From this viewpoint, the thickness of the release layer is preferably 0.005 μm to 1 μm, more preferably 0.02 μm or more or 0.5 μm or less, and even more preferably 0.045 μm or more or 0.085 μm or less.

(Method of forming the release layer)
The present release layer can be formed from a resin composition (also referred to as the "present release layer forming composition") that contains a silicone compound, a compound containing a (meth)acryloyl group, and, if necessary, a catalyst, particularly a platinum group metal catalyst, a catalyst activity inhibitor, etc.
However, the detailed method for forming the release layer using the release layer-forming composition will be described later, and the release layer-forming composition will be described here.

(Silicone Compound)
The silicone compound has been generally described above.
Among the above, the silicone compound used in the present release layer-forming composition preferably contains a curable silicone compound in consideration of heat resistance and contamination resistance.
As the type of curable silicone compound, any curing reaction type can be used, such as addition curing type, condensation curing type, ultraviolet curing type, electron beam curing type, etc. Among them, addition curing type silicone compounds are more preferred from the viewpoint of being able to increase the cohesive strength of the coating film.

An addition-curing silicone compound is a silicone compound that has unsaturated hydrocarbon groups and hydrogen groups as functional groups in its structure, and the addition curing reaction occurs through the reaction of these functional groups. That is, it is a mixture of a silicone compound having a Si-H group and a silicone compound containing an alkenyl group, or a silicone compound that contains a Si-H group and a vinyl group in the molecule.
From the viewpoint of pot life, it is preferable that the unsaturated hydrocarbon group and the hydrogen group are not present in the same molecule, and it is preferable to use a mixture of functional groups contained in separate silicone molecules.Therefore, it is preferable to use a mixture of a silicone compound having an unsaturated hydrocarbon group as a functional group and a silicone compound having a hydrogen group as a functional group.

An example of the silicone compound having an unsaturated hydrocarbon group as a functional group is polydimethylsiloxane containing an unsaturated hydrocarbon group.
At least two unsaturated hydrocarbon groups must be contained in the polydimethylsiloxane molecule. Examples of the unsaturated hydrocarbon group include alkenyl groups having 2 to 8 carbon atoms, such as vinyl groups, propenyl groups, butenyl groups, and pentenyl groups. Among these, vinyl groups are preferred because of their ease of industrial availability.
The at least two alkenyl groups may have different numbers of carbon atoms.
The polydimethylsiloxane containing an unsaturated hydrocarbon group has an alkenyl group and a methyl group as functional groups directly bonded to a silicon atom, and may also have various other functional groups. Examples of functional groups other than the methyl group include alkyl groups such as ethyl, propyl, and butyl groups, cycloalkyl groups such as cyclohexyl groups, aryl groups such as phenyl and methylphenyl groups, and alkoxy groups such as hydroxy, methoxy, and ethoxy groups. From the viewpoint of adhesion to polyester films, it is preferable to include a phenyl group or a methoxy group.

On the other hand, the silicone compound having a hydrogen group as a functional group can be exemplified by a polydimethylsiloxane containing a hydrogen group. A polydimethylsiloxane containing a hydrogen group is a polydimethylsiloxane having a hydrogen atom bonded to a silicon atom. It is necessary that one molecule contains at least two hydrogen atoms bonded to a silicon atom, and it is preferable that one molecule contains three or more hydrogen atoms from the viewpoint of curing properties. The hydrogen atom bonded to silicon may be at the end or side chain of the polydimethylsiloxane molecular chain.
Hydrogen-containing polydimethylsiloxane has hydrogen and methyl groups as functional groups directly bonded to silicon atoms, but may also have various other functional groups. Examples of functional groups other than methyl groups include alkyl groups such as ethyl, propyl, and butyl groups, cycloalkyl groups such as cyclohexyl groups, aryl groups such as phenyl and methylphenyl groups, hydroxy groups, and alkoxy groups such as methoxy and ethoxy groups.

The polydimethylsiloxane skeleton of the polydimethylsiloxane containing an unsaturated hydrocarbon group and the polydimethylsiloxane containing a hydrogen group may each be linear or branched.

The blend of the unsaturated hydrocarbon-containing polydimethylsiloxane and the hydrogen group-containing polydimethylsiloxane is preferably such that the molar ratio of all Si--H groups to all alkenyl groups (Si--H group amount/alkenyl group amount) is 1.0 to 5.0.
When the molar ratio is 1.0 or more, the curability can be maintained, and when it is 5.0 or less, the amount of remaining Si-H groups is not too large, and the peel force from the adhesive does not become too strong, so this is preferable.
From this viewpoint, it is preferably 1.0 to 5.0, more preferably 1.6 or more or 4.8 or less, and even more preferably 2.0 or more or 4.6 or less.

The silicone compound used in the release layer-forming composition may be a solvent-curable silicone or a solventless-curable silicone. A mixture of a solvent-curable silicone and a solventless-curable silicone may also be used.
Whether the silicone is a solvent-curable silicone or a solventless-curable silicone, it is preferably a curable silicone that has releasability and that involves an addition reaction between a vinyl group and a group having a silicon-hydrogen bond during the curing process (so-called addition silicone).

From the viewpoints of the working environment and safety, such as the risk of organic solvent explosion and fire, the coating liquid used to form the release layer preferably contains water as the main solvent, and the above-mentioned silicone compound is preferably used as a silicone emulsion.
When water is used as the main solvent, it is preferable that water accounts for 80% by mass or more of the solvent, more preferably 90% by mass or more, and even more preferably 95% by mass or more of the solvent.
When the silicone compound is emulsified, a surfactant component can be used as an emulsion stabilizer.

The surfactant may be a nonionic surfactant or an anionic surfactant.
Examples of nonionic surfactants include polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers, polyoxyalkylene phenyl ethers such as polyoxyethylene phenyl ethers, glycerin alkyl ethers, glycerin fatty acid esters and their alkylene glycol adducts, polyglycerin fatty acid esters and their alkylene glycol adducts, propylene glycol fatty acid esters and their alkylene glycol adducts, polyalkylene glycol fatty acid esters, etc. Examples of anionic surfactants include fatty acid soaps such as sodium stearate and triethanolamine palmitate, alkyl ether carboxylic acids and their salts, alkyl sulfonic acids, alkene sulfonates, sulfonates of fatty acid esters, alkyl sulfates, secondary higher alcohol sulfates, alkyl and allyl ether sulfates, fatty acid ester sulfates, polyoxyethylene alkyl sulfates, sulfates such as turpentine oil, alkyl phosphates, ether phosphates, alkyl allyl ether phosphates, amide phosphates, etc. Of these, nonionic surfactants are preferred, and from the standpoint of the stability of the silicone emulsion, polyoxyalkylene alkyl ethers and polyoxyalkylene phenyl ethers are more preferred.

Examples of polyoxyalkylene alkyl ethers include polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, and polyoxybutylene alkyl ethers. Of these, polyoxyethylene alkyl ethers are preferred. The alkyl group is preferably a straight-chain or branched alkyl group having 8 to 30 carbon atoms, and more preferably a straight-chain or branched alkyl group having 8 to 16 carbon atoms.

Examples of polyoxyalkylene phenyl ethers include polyoxyethylene phenyl ether, polyoxypropylene phenyl ether, and polyoxybutylene phenyl ether. Among these, polyoxyethylene alkyl ethers are preferred. Furthermore, the phenyl group is preferably an unsubstituted or substituted phenyl group, and is preferably a styrenated phenyl group in which the hydrogen atom of the phenyl group is substituted with a styryl group.

(Compound containing a (meth)acryloyl group)
The compound containing a (meth)acryloyl group contained in the present release layer-forming composition is as described above.

The content of the compound containing a (meth)acryloyl group contained in the present release layer forming composition is preferably 1 to 50 mass % as a ratio to the total non-volatile components in the present release layer forming composition.
If the content of the compound containing a (meth)acryloyl group is 1% by mass or more, the adhesion of the release layer to the polyester film can be obtained, and if it is 50% by mass or less, excellent release properties can be obtained.
From this viewpoint, the content of the compound containing the (meth)acryloyl group is preferably 1 to 50 mass % as a ratio to the total non-volatile components in the release layer forming composition, and more preferably 1 mass % or more or 40 mass % or less, and even more preferably 2 mass % or more or 30 mass % or less.

The content of the compound containing a (meth)acryloyl group contained in the release layer-forming composition is preferably 1 to 100 parts by mass with respect to 100 parts by mass of the silicone compound.
If the content of the compound containing the (meth)acryloyl group is 1 part by mass or more, it is preferable from the viewpoint of obtaining adhesion of the release layer to the polyester film, and if it is 100 parts by mass or less, it is preferable from the viewpoint of excellent release properties.
From this viewpoint, the content of the compound containing a (meth)acryloyl group is preferably 1 to 100 parts by mass, more preferably 1 part by mass or more or 65 parts by mass or less, and even more preferably 2 parts by mass or more or 40 parts by mass or less, relative to 100 parts by mass of the silicone compound.

(Platinum Group Metal Catalyst)
The release layer-forming composition may also contain a catalytic amount of a platinum group metal catalyst.
The platinum group metal catalyst is a catalyst for accelerating the curing reaction of silicone compounds, for example, an addition curing reaction, and any of the conventionally known addition reaction catalysts can be used.

Examples of the platinum group metal catalyst include platinum-based, palladium-based, and rhodium-based catalysts, among which platinum-based catalysts are preferred.
Examples of the platinum catalyst include chloroplatinic acid, alcohol solutions or aldehyde solutions of chloroplatinic acid, and complexes of chloroplatinic acid with various olefins or vinylsiloxanes.
From the viewpoint of pot life, the timing of blending the platinum group metal catalyst is preferably within 20 hours immediately before coating the present release layer-forming composition, and more preferably within 10 hours.

The amount of platinum group metal catalyst in the release layer relative to the silicone compound is preferably in the range of 1 to 1000 ppm, and more preferably in the range of 20 ppm or more or 800 ppm or less. This range makes it possible to adequately achieve both the promotion of the addition curing reaction and a long pot life.

(Other added ingredients)
If necessary, the release layer forming composition may also contain reactive release adjusters, diluting solvents, reaction adjusters, adhesion enhancers, acetylene derivatives, various organic nitrogen compounds, various phosphorus compounds, oxime compounds, organic halogen compounds and other catalytic activity inhibitors, oxazoline compounds, epoxy compounds, silane coupling agents and other crosslinking agents, particles, defoamers, coatability improvers, thickeners, organic lubricants, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, and the like.

The reactive release strength regulator is a type of release strength regulator that reacts with the siloxane polymer of the release coating when the coating is dried and is incorporated therein.
The reactive high release regulator preferably has a chemical structure having, for example, a vinyl group as a reactive group, and is generally called an MQ resin or an MDQ resin.

Examples of dilution solvents include aromatic hydrocarbons such as toluene, aliphatic hydrocarbons such as hexane, heptane, isooctane, esters such as ethyl acetate and butyl acetate, ketones such as ethyl methyl ketone (MEK) and isobutyl methyl ketone, alcohols such as ethanol and 2-propanol, and ethers such as diisopropyl ether and dibutyl ether. These are preferably used alone or in combination, taking into consideration solubility, coatability, boiling point, etc.

<Layer structure of this release film>
The present release film may have the present release layer on one or both sides of the present polyester film, and may therefore have a laminated structure in which the present release layer is laminated on one or both sides of the present polyester film, or may have another layer on the surface side of the present release layer, or may have the present release layer laminated on one side of the present polyester film and another layer on the other side.

Examples of the "other layer" include an antistatic layer, an oligomer sealing layer, an adhesive layer, and a release layer having a composition different from that of the release layer.
An example of the laminated configuration of the present release film is a laminated configuration in which the present release layer is laminated on one side of the present polyester film, and an antistatic layer, an oligomer sealing layer, and an adhesive layer are laminated on the other side.

The antistatic layer may contain an electronically conductive compound.
Examples of the electronically conductive organic compound include ammonium group-containing compounds, polyacetylene, polyphenylene, polyaniline, polypyrrole, polyisothianaphthene, and polythiophene, etc. Among these, polythiophene, i.e., a polymer obtained by homopolymerizing or copolymerizing thiophene or a thiophene derivative, can be given.
In addition to the electronically conductive compound, the antistatic layer may contain one or more compounds selected from the group consisting of polyalkylene oxides, glycerin, polyglycerin, and alkylene oxide adducts to glycerin or polyglycerin, or derivatives thereof.

When the antistatic layer is formed by coating, the coating liquid may contain, for example, a surfactant, other binders, particles, a defoaming agent, a coatability improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, etc. These additives may be used alone, or two or more of them may be used in combination as necessary.
Furthermore, the polyester film as the substrate may be subjected to a chemical treatment, a corona discharge treatment, a plasma treatment, or the like before coating.

The oligomer sealing layer is preferably a coating layer formed from a coating system containing 70% by mass or more of a crosslinking agent as a non-volatile component, or a layer containing a hydrolyzable alkoxysilicate and/or a polycondensate thereof.

As the crosslinking agent, various known crosslinking agents can be used, such as oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, etc.

The hydrolyzable alkoxysilicates include those having a structure represented by the general formula Si(OR ₁ ) ₄ (R1 represents a hydrocarbon group having 1 to 10 carbon atoms).
The oligomer sealing layer may further contain inorganic particles, and specific examples of the inorganic particles include silica, alumina, kaolin, calcium carbonate, titanium oxide, and barium salts.
The oligomer sealing layer may also contain antifoaming agents, coating property improvers, thickeners, organic lubricants, organic polymer particles, antioxidants, ultraviolet absorbers, foaming agents, dyes, and the like.

The adhesive layer contains an adhesive composition. The adhesive composition can be used without any particular limitation as long as it can provide adhesiveness, and examples thereof include acrylic adhesives, urethane adhesives, rubber adhesives, and silicone adhesives. Among these, acrylic adhesives are preferred from the viewpoint of easy adjustment of adhesive properties and excellent transparency. In addition, examples of the adhesive forming method include heat curing type, active energy ray curing type, and hot melt type.
When forming an adhesive layer by coating, the coating liquid may contain, for example, a binder, a crosslinking agent, a surfactant, particles, an antifoaming agent, a coatability improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, etc. These additives may be used alone, or two or more of them may be used in combination as necessary.

<Method of manufacturing the release film>
The present release film can be produced by applying the present release layer forming composition, which contains a silicone compound and a compound containing a (meth)acryloyl group, to one or both sides of the present polyester film, and forming the above-mentioned "other layers" such as an antistatic layer, oligomer sealing layer, or adhesive layer as necessary, or by curing treatment at any stage of these to form the present release layer, and further heat treating as necessary.

Prior to applying the release layer-forming composition, the polyester film may be subjected to a surface treatment such as a corona treatment or a plasma treatment. Furthermore, the polyester film may be provided with a coating layer such as an adhesive layer in advance.

The energy source for the curing process is generally heat treatment. However, ultraviolet irradiation and electron beam irradiation can also be used in combination.

The method for forming the release layer, i.e., the method for applying the release layer-forming composition, may be in-line coating or offline coating.

Among these, it is preferable to form the release layer by using in-line coating.
In-line coating is a method of coating within the process of producing a polyester film. Specifically, it is a method of coating at any stage from melt extrusion of polyester to stretching, heat setting and winding up. Usually, the coating is performed on any of the following: an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, and a film after heat setting and before winding up.

In the method for producing the present release film, it is preferable to form the present release layer during the process of producing the present polyester film, and then stretch the film.
For example, in the case of sequential biaxial stretching, it is preferable to apply the release layer forming composition to a uniaxially stretched film that has been stretched in the longitudinal direction (machine direction), and then stretch the film in the transverse direction. According to this method, the polyester film and the release layer can be formed simultaneously, which is advantageous in terms of production costs. Furthermore, since stretching is performed after coating, the thickness of the release layer can be changed by the stretching ratio, and thin film coating can be performed more easily compared to offline coating. Furthermore, by providing the release layer on the film before stretching, the release layer can be stretched together with the polyester film, and the release layer can be firmly attached to the polyester film. Furthermore, in the production of biaxially stretched polyester film, the film can be restrained in the machine direction and the transverse direction by stretching while holding the film end with a clip or the like, and high temperature can be applied in the heat fixing process while maintaining the flatness without wrinkles or the like. Therefore, the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, which improves the film-forming properties of the release layer and enables the release layer to adhere more firmly to the polyester film, thereby making the release layer stronger and improving the performance and durability of the release layer.

When providing the release layer by in-line coating, it is preferable to coat the release layer-forming composition described above as an aqueous solution or aqueous dispersion onto the polyester film as a coating liquid adjusted to a solids concentration of approximately 0.1 to 50 mass %.
Furthermore, within the scope of the present invention, a small amount of an organic solvent may be contained in the coating solution for the purpose of improving dispersibility in water, improving film-forming properties, etc. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

The method for applying the release layer-forming composition may be a conventionally known coating method such as multi-roll coating, gravure coating, reverse gravure coating, reverse roll coating, direct gravure coating, die coating, air doctor coating, blade coating, rod coating, bar coating, curtain coating, knife coating, transfer roll coating, squeeze coating, impregnation coating, kiss coating, spray coating, calendar coating, extrusion coating, etc. For example, a coating technique such as that shown in "Coating Methods" (Yuji Harasaki, Maki Shoten, published in 1979) may be used.
Examples of the coating head used in this case include an air doctor coater, blade coater, rod coater, knife coater, squeeze coater, impregnation coater, reverse roll coater, transfer roll coater, gravure coater, kiss roll coater, cast coater, spray coater, curtain coater, calendar coater, and extrusion coater.

After forming the release layer as described above, it is preferable to heat the release layer to 70°C or higher, preferably 80°C or higher or 270°C or lower, more preferably 100°C or higher or 270°C or lower, and more preferably 180°C or higher, to dry or harden the release layer.
In particular, when the release layer is provided by off-line coating, it is preferable to carry out heat treatment at 80 to 200° C. for 3 to 40 seconds, preferably at 100 to 180° C. for 3 to 40 seconds.
On the other hand, when providing the release layer by in-line coating, it is preferable to carry out heat treatment at 70 to 270°C for 3 to 200 seconds, preferably at 180°C or higher, and particularly at 180 to 270°C for 3 to 200 seconds as a guideline, and the heat treatment may be carried out together with the above-mentioned heat fixing step of the film.

Regardless of whether off-line coating or in-line coating is used, heat treatment and irradiation with active energy rays such as ultraviolet rays may be used in combination, if necessary.
The polyester film may be previously subjected to a surface treatment such as a corona treatment or a plasma treatment.

<Characteristics of this release film>
The release film can have a 180° peel strength of 200 mN/cm or less, preferably 100 mN/cm or less, and more preferably 50 mN/cm or less, measured under conditions of a pulling speed of 0.3 m/min after attaching an acrylic adhesive tape (Nitto Denko Corporation, No. 502) to the release layer and leaving it at room temperature for 1 hour. There is no lower limit to this peel strength, and specifically it is 0.1 mN/cm or more.

This release film is prepared by attaching a BEMCOT ("M-3II" manufactured by Asahi Kasei Fibers Corporation) impregnated with 4 mL of toluene to a rubbing tester (manufactured by Ohira Rika Kogyo Co., Ltd.) and rubbing the release layer surface of the sample film 10 times with an arm load of 680 g to perform a solvent treatment, and then attaching an acrylic adhesive tape (No. 502 manufactured by Nitto Denko Corporation) to this release layer and leaving it at room temperature for 1 hour, and then the 180° peel strength measured under the condition of a tensile speed of 0.3 m/min can be 300 mN/cm or less, preferably 200 mN/cm or less, and more preferably 100 mN/cm or less. There is no lower limit to this peel strength, and specifically it is 0.1 mN/cm or more.
The present release film can maintain excellent releasability even after the solvent treatment.

This release film is stored for one month in an environment of 23°C and 50% RH with an untreated polyester film superimposed on the release layer surface of the film, and then the release layer surface is subjected to a solvent treatment. After that, an acrylic adhesive tape (Nitto Denko Corporation, No. 502) is attached to this release layer and left at room temperature for one hour, and the 180° peel force measured under conditions of a tensile speed of 0.3 m/min can be reduced to 800 mN/cm or less, preferably 500 mN/cm or less, and more preferably 350 mN/cm or less.
The present release film can maintain excellent releasability even after solvent treatment following such long-term storage.

The release film can have a residual adhesion rate, which is the ratio of "F1/F0" measured as follows using an acrylic adhesive tape (Nitto Denko Corporation, No. 31B), of 80% or more, preferably 85% or more, more preferably 90% or more, and even more preferably 93% or more. The upper limit of this residual adhesion rate is 100%.
F1: The above adhesive tape is attached to the release layer of this release film and heat-treated at 100° C. for 1 hour, then the release film is peeled off and the remaining adhesive tape is attached to a stainless steel plate, and the 180° peel force is measured under conditions of a tensile speed of 0.3 m/min. F0: The above adhesive tape is attached directly to a stainless steel plate, and the 180° peel force is measured in the same manner as F1. In this way, this release film can obtain low contamination properties for the adhesive layer.

<Applications of this release film>
This release film not only has excellent releasability, solvent resistance even after long-term storage, and low contamination, but also provides excellent adhesion to plastic substrates and excellent coating appearance (evenness).
Therefore, the present release film can be suitably used in the manufacture of liquid crystal display devices used as image display devices such as liquid crystal televisions, computer displays, mobile phones, and digital cameras, and in the manufacture of ceramic capacitors.
To give a specific example, an adhesive layer is laminated on the release layer of the release film to produce a release film with an adhesive layer, and the adhesive layer is attached to a polarizing plate to produce a polarizing plate with an adhesive layer.When bonding the polarizing plate to a liquid crystal cell, the base film is peeled off and the adhesive layer and the glass substrate of the liquid crystal cell are attached to produce the polarizing plate.
It is also effective in producing a release film with an adhesive layer formed by using a solvent-containing adhesive resin composition.

<<Terminology explanation>>
Generally, a "sheet" is defined in the JIS as a thin, flat product whose thickness is small relative to its length and width, and a "film" is generally a thin, flat product whose thickness is extremely small relative to its length and width and whose maximum thickness is arbitrarily limited, and which is usually supplied in the form of a roll (Japanese Industrial Standard JIS K6900). However, the boundary between a sheet and a film is unclear, and there is no need to distinguish between the two in the present invention, so in the present invention, the term "film" includes "sheet", and the term "sheet" includes "film".

In the present invention, when it is described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably larger than X" or "preferably smaller than Y".
In addition, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples without departing from the gist of the present invention.
The measurement and evaluation methods used in the present examples are as follows.

(1) Method for Measuring the Intrinsic Viscosity of Polyester 1 g of polyester from which components incompatible with the polyester had been removed was precisely weighed, dissolved in 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio), and the intrinsic viscosity was measured at 30°C.

(2) Measurement of average particle size (d50) The particle size at an integrated volume fraction of 50% in the equivalent sphericity distribution measured using a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type) manufactured by Shimadzu Corporation was taken as the average particle size d50.

(3) Method for Measuring Film Thickness of Release Layer The surface of the release layer was stained with _RuO4 and embedded in epoxy resin. Then, a slice prepared by ultra-thin sectioning was stained with _RuO4 , and the cross section of the release layer was measured using a transmission electron microscope (Hitachi High-Technologies Corporation H-7650, accelerating voltage 100 kV).

(4) Evaluation of peeling force of release film One side of a double-sided adhesive tape ("No. 502" manufactured by Nitto Denko Corporation) cut to a width of 5 cm was pressed back and forth once with a 2 kg rubber roller onto the release layer surface of the sample film, and the peeling force was measured after leaving it at room temperature for 1 hour. The peeling force was measured using "Ezgraph" manufactured by Shimadzu Corporation, and 180° peeling was performed under the condition of a pulling speed of 300 mm/min. In the table, this peeling force is shown as "initial".
An "initial" peel strength of 200 mN/cm or less is preferred.

(5) Evaluation of peel strength after heating of release film One side of a double-sided adhesive tape ("No. 502" manufactured by Nitto Denko Corporation) cut to a width of 5 cm was pressed once back and forth on the release layer surface of the sample film with a 2 kg rubber roller, and then heated in an oven at 100°C for 1 hour. The peel strength was then measured after leaving it at room temperature for 1 hour. The peel strength was measured using "Ezgraph" manufactured by Shimadzu Corporation, and 180° peeling was performed under the condition of a tensile speed of 300 mm/min. In the table, this peel strength is shown as "after heating".

(6) Evaluation of peeling force after solvent treatment of release film An untreated polyester film was superposed on the release layer surface of the sample film, and one week after the film was prepared, the untreated polyester film was peeled off, and a BEMCOT ("M-3II" manufactured by Asahi Kasei Fibers Corporation) impregnated with 4 mL of toluene was attached to a rubbing tester (manufactured by Ohira Rika Kogyo Co., Ltd.) and reciprocated 10 times on the release layer surface of the sample film with an arm load of 680 g. After air drying, one side of a double-sided adhesive tape ("No. 502" manufactured by Nitto Denko Corporation) cut to a width of 5 cm was pressed once with a 2 kg rubber roller, and the peeling force was measured after leaving it at room temperature for 1 hour. The peeling force was measured by 180° peeling at a tensile speed of 300 mm/min using "Ezgraph" manufactured by Shimadzu Corporation. In the table, this peeling force is shown as "after solvent treatment".
A peel strength after solvent treatment of 300 mN/cm or less is preferred.

(7) Evaluation of peel strength after solvent treatment after one month of release film After storing the sample film for one month in an environment of 23°C and 50% RH with an untreated polyester film superimposed on the release layer surface, the untreated polyester film was peeled off from the release film, and the release film was used to perform 180° peeling in the same manner as the peel strength after "solvent treatment" described above. This peel strength is shown in the table as "after one month of solvent treatment".
A peel strength of 800 mN/cm or less after "one month and solvent treatment" is preferred.

(8) Evaluation of residual adhesion rate of release film An adhesive tape "No. 31B" (manufactured by Nitto Denko Corporation) was pressed once back and forth on the surface of the release layer with a 2 kg rubber roller, and heat-treated at 100°C for 1 hour. Next, the pressed release film was peeled off, and the remaining adhesive tape "No. 31B" was used to measure the adhesive strength F1 according to the method of JIS-C2107 (adhesive strength to stainless steel plate, 180° peeling method). The percentage of F1 relative to the adhesive strength F0 when the adhesive tape "No. 31B" was directly adhered to and peeled off from the stainless steel plate was taken as the residual adhesion rate.
A residual adhesion rate close to 100% is preferred.

Next, we will explain the materials used in the examples and comparative examples.

<Polyester (A)>
Polyethylene terephthalate homopolymer with an intrinsic viscosity of 0.63

<Polyester (B)>
A polyethylene terephthalate homopolymer having an intrinsic viscosity of 0.65 and containing 0.2% by mass of silica particles having an average particle size of 2 μm.

<Vinyl Group-Containing Polydimethylsiloxane (IA)>
Aqueous dispersion of vinyl-containing polydimethylsiloxane with a vinyl group content of 0.16 mmol/g (emulsifier: nonionic surfactant)

<Hydrogen-containing polydimethylsiloxane (IIA)>
Aqueous dispersion of hydrogen-containing polydimethylsiloxane with a Si-H group content of 6.6 mmol/g (emulsifier: nonionic surfactant)

<Hydrogen-containing polydimethylsiloxane (IIB)>
Aqueous dispersion of hydrogen-containing polydimethylsiloxane with a Si-H group content of 8.1 mmol/g (emulsifier: nonionic surfactant)

<Hydrogen-containing polydimethylsiloxane (IIC)>
Aqueous dispersion of hydrogen-containing polydimethylsiloxane with a Si-H group content of 12.7 mmol/g (emulsifier: nonionic surfactant)

<Acryloyl Group-Containing Compound (IIIA)>
A water dispersion of a mixture of 50 parts by mass of urethane (meth)acrylate formed from a polyhexamethylene carbonate diol unit having a molecular weight of 1,100:dimethylolpropanoic acid unit:hydrogenated xylylene diisocyanate unit:dipentaerythritol pentaacrylate unit=11:7:40:42 (mol %), 27 parts by mass of dipentaerythritol hexaacrylate, and 23 parts by mass of trimethylolpropane triacrylate, the mixture being a mixture of (meth)acrylate compounds other than urethane (meth)acrylate and urethane (meth)acrylate.

<Acryloyl Group-Containing Compound (IIIB)>
A water-dispersed composite resin (mass ratio of acryloyl groups to composite resin: 14% by mass (solid ratio)) was prepared by mixing and dispersing a cresol novolac epoxy resin into which an acryloyl group had been introduced (acryloyl group: cresol novolac epoxy resin monomer = 1:1.1 (mol %)) and a polyester-based urethane resin formed from isophorone diisocyanate: terephthalic acid: isophthalic acid: ethylene glycol: diethylene glycol: dimethylolpropanoic acid = 12:19:18:21:25:5 (mol %) in a solid content mass ratio of 1.0:1.0 to form a core-shell structure (resin containing an acryloyl group in the core, urethane resin in the shell).

<Acrylic resin (IVA)>
Aqueous dispersion of acrylic resin polymerized with the following composition: Emulsion polymer of ethyl acrylate/n-butyl acrylate/methyl methacrylate/N-methylolacrylamide/acrylic acid = 65/21/10/2/2 (mass%) (emulsifier: anionic surfactant)

<Urethane resin (IVB)>
A water dispersion of a urethane resin obtained by neutralizing a prepolymer consisting of 400 parts of polycarbonate polyol having a number average molecular weight of 2000, consisting of 1,6-hexanediol and diethyl carbonate, 10.4 parts of neopentyl glycol, 58.4 parts of isophorone diisocyanate, and 7.4 parts of dimethylolbutanoic acid with triethylamine and chain-extending with isophorone diamine.

<Platinum Group Metal Catalyst (V)>
Complexes of chloroplatinic acid with vinylsiloxanes.

Example 1
The mixed raw material obtained by mixing polyesters (A) and (B) at a ratio of 90% by mass and 10% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and only polyester (A) was used as the raw material for the intermediate layer. Each was fed to two extruders, melted at 285 ° C., and then co-extruded on a cooling roll set at 40 ° C. with a layer structure of two types and three layers (surface layer / intermediate layer / surface layer = 1: 8: 1 discharge amount) and cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85 ° C. using the roll peripheral speed difference, and then a coating liquid having the composition shown in Table 1 below was applied to one side of this longitudinally stretched film, introduced into a tenter, stretched 4.3 times in the transverse direction at 110 ° C., and heat-treated at 235 ° C., and then relaxed 2% in the transverse direction to obtain a release film (sample) having a thickness of 50 μm and a release layer with a film thickness (after drying) of 0.06 μm.

The polyester film obtained was evaluated and found to have good releasability even after one month of solvent treatment. The properties of this film are shown in Table 2 below.

<Examples 2 to 21>
A polyester film was obtained in the same manner as in Example 1, except that the coating agent composition in Example 1 was changed to the coating agent composition shown in Table 1.
As shown in Table 2, the polyester film obtained had good releasability and residual adhesion after one month of solvent treatment.

<Comparative Example 1>
A polyester film was obtained in the same manner as in Example 1, except that no coating layer was provided.
The polyester film thus obtained was evaluated, and as shown in Table 2, it was found to have poor releasability.

<Comparative Examples 2 to 6>
A polyester film was obtained in the same manner as in Example 1, except that the coating agent composition in Example 1 was changed to the coating agent composition shown in Table 1.
The polyester film thus obtained was evaluated, and as shown in Table 2, it was found to be poor in releasability after one month of solvent treatment, residual adhesion rate, initial peel properties, etc.

From the above examples and comparative examples and the results of various tests conducted by the inventors, it has been confirmed that by adding a compound containing a (meth)acryloyl group in addition to a silicone compound to the release layer laminated to the polyester film (substrate), the adhesion between the polyester film (substrate) and the release layer can be favorably maintained even when the release layer comes into contact with a solvent.

The release film of the present invention is a release film that is less susceptible to deterioration in releasability due to solvents used in processing the adhesive layer, even after long-term storage, and can be suitably used, for example, as a release film for adhesives or a protective film for the adhesive layer of a polarizing plate.

Claims (20)

A release film comprising a release layer on at least one side of a polyester film, the release layer comprising a silicone compound and a compound containing a (meth)acryloyl group;
the silicone compound is an organopolysiloxane having a Si—H group, and is contained in the release layer in an amount of 70 to 99% by mass;
The content of the compound containing a (meth)acryloyl group is 1 to 65 parts by mass based on 100 parts by mass of the silicone compound. However, the release film according to claim 1 does not include a photopolymerization initiator. A release film comprising a release layer on at least one side of a polyester film, the release layer being a layer formed from a release-layer-forming composition containing a silicone compound and a compound containing a (meth)acryloyl group;
the silicone compound is an organopolysiloxane having a Si—H group, and is contained in the release layer in an amount of 70 to 99% by mass;
The content of the compound containing a (meth)acryloyl group is 1 to 65 parts by mass based on 100 parts by mass of the silicone compound. The release film according to claim 3, wherein the release layer is a layer formed by curing the release layer-forming composition by heat treatment. The release film according to any one of claims 1 to 4, wherein the compound containing a (meth)acryloyl group is a urethane (meth)acrylate, or a mixture of a urethane (meth)acrylate and a (meth)acrylate compound other than a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin. The release film according to any one of claims 1 to 5, wherein the compound containing a (meth)acryloyl group is a mixture of a urethane (meth)acrylate and a (meth)acrylate compound other than a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin. The release film according to any one of claims 1 to 6, wherein the silicone compound is a silicone compound having a Si-H group and an alkenyl group. The release film according to any one of claims 1 to 7 , wherein the silicone compound comprises a vinyl group-containing polydimethylsiloxane. The release film according to any one of claims 1 to 8 , wherein the silicone compound comprises a vinyl group-containing polydimethylsiloxane and a hydrogen group-containing polydimethylsiloxane. The release film according to any one of claims 1 to 9, wherein the compound containing a (meth)acryloyl group is contained in the release layer in an amount of 1 to 30% by mass. A method for producing a release film, comprising applying a release layer-forming composition containing a silicone compound and a compound containing a (meth)acryloyl group to at least one side of a polyester film to form a release layer,
the silicone compound is an organopolysiloxane having a Si—H group, and is contained in the release layer in an amount of 70 to 99% by mass;
The content of the compound containing a (meth)acryloyl group is 1 to 65 parts by mass based on 100 parts by mass of the silicone compound. The method for producing a release film according to claim 11 , wherein the release layer-forming composition is applied and cured by heat treatment to form a release layer. The method for producing a release film according to claim 11 or 12 , characterized in that, in the process of producing the polyester film, after the release layer is formed, the polyester film is stretched. The method for producing a release film according to any one of claims 11 to 13 , characterized in that after the release layer is formed, the release layer is heated to 180°C or higher. The method for producing a release film according to any one of claims 11 to 14, wherein the compound containing a (meth)acryloyl group is a urethane (meth)acrylate, or a mixture of a urethane (meth)acrylate and a (meth)acrylate compound other than a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin. The method for producing a release film according to any one of claims 11 to 15, wherein the compound containing a (meth)acryloyl group is a mixture of a urethane (meth)acrylate and a (meth)acrylate compound other than a urethane (meth)acrylate, or a composite resin of an epoxy (meth)acrylate and a urethane resin. The method for producing a release film according to any one of claims 11 to 16, wherein the silicone compound is a silicone compound having a Si-H group and an alkenyl group. The content of the compound containing a (meth)acryloyl group is 1 to 30 mass% as a ratio to the total non-volatile components in the release layer forming composition. The method for producing a release film according to any one of claims 11 to 17. A pressure-sensitive adhesive sheet with a release film, comprising a release layer of the release film according to any one of claims 1 to 10 and a pressure-sensitive adhesive layer laminated thereon. A method for producing an adhesive sheet with a release film, comprising applying a solvent-containing adhesive composition to the release layer of the release film according to any one of claims 1 to 10 to form an adhesive layer.