Mold release coating agent for polyester base materials, mold release sheet, and multilayer body

Abstract

The present invention provides a mold release coating agent for polyester base materials, the mold release coating agent having excellent adhesiveness to a polyester base material and heat-resistant releasability. A mold release coating agent for polyester base materials according to one embodiment of the present invention contains an aqueous dispersion that is obtained by dispersing a polyurethane resin into an aqueous dispersion medium. The aqueous dispersion contains a (meth) acrylic polymer which contains, as constituent components, a monofunctional alkyl (meth) acrylate that has an alkyl group having 4 to 22 carbon atoms, and a poly (meth) acrylate that has 2 to 6 functional groups.

Description

Release coating agent for polyester substrate, release sheet and laminate

[0001] An embodiment of the present invention relates to a release coating agent that is applied to a polyester substrate, and a release sheet and a laminate obtained by using the release coating agent.

[0002] Release sheets (also referred to as release sheets) are known in which a release layer is formed by applying a release coating agent to a polyester substrate such as a polyester film. For example, Patent Document 1 discloses a release agent composition containing a silicone resin, an alkoxy group-containing silane-modified polyurethane resin, and a solvent as a release coating agent that is applied to the surface of a release base substrate to form a release layer. Such release coating agents include not only silicone-based but also non-silicone-based release coating agents that can prevent silicone migration.

[0003] JP 2011-099095 A

[0004] A release coating agent that is applied to a polyester substrate is required to have adhesion to the polyester substrate, and also to be easily peelable from a resin layer, such as a pressure-sensitive adhesive film to be protected as a release sheet or a resin film formed on the release sheet, i.e., to have peelability from the resin layer. In this case, the laminate of the release sheet and the resin layer may be placed in a heated atmosphere, so it is desirable for the release coating agent to be peelable even after heat treatment, i.e., to have heat-resistant peelability.

[0005] An object of an embodiment of the present invention is to provide a release coating agent for polyester substrates that has excellent adhesion to polyester substrates and heat-resistant peelability.

[0006] The present invention includes the following embodiments. [1] A release coating agent for polyester substrates, comprising an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, the aqueous dispersion comprising a (meth)acrylic polymer containing, as constituent components, a monofunctional alkyl (meth)acrylate having an alkyl group with 4 to 22 carbon atoms and a poly(meth)acrylate having 2 to 6 functional groups. [2] The release coating agent for polyester substrates according to [1], wherein the (meth)acrylic polymer is contained together with the polyurethane resin in individual resin particles as a dispersoid. [3] The release coating agent for polyester substrates according to [1] or [2], wherein the (meth)acrylic polymer comprises 0.3 to 50 parts by mass of the poly(meth)acrylate per 100 parts by mass of the alkyl (meth)acrylate. [4] The release coating agent for polyester substrates according to any one of [1] to [3], wherein the alkyl group of the alkyl (meth)acrylate is a linear alkyl group. [5] The release coating agent for polyester substrates according to any one of [1] to [4], wherein the poly(meth)acrylate has an acrylic equivalent, which is the molecular weight per functional group, of 80 to 150. [6] The release coating agent for polyester substrates according to any one of [1] to [5], wherein the amount of the alkyl (meth)acrylate per 100 parts by mass of the polyurethane resin is 40 to 350 parts by mass. [7] The release coating agent for polyester substrates according to any one of [1] to [6], wherein the polyurethane resin contains a polyol, including a polyester polyol, as a constituent component, and the polyester polyol is contained in an amount of 30% by mass or more per 100% by mass of the polyol.

[0007] [8] A release sheet comprising a polyester substrate and a release layer formed on the polyester substrate, the release layer comprising the release coating agent according to any one of [1] to [7]. [9] A laminate comprising the release sheet according to [8] and a resin layer releasably formed on the release layer of the release sheet.

[0008]

[10] A release coating agent for polyester substrates, comprising an aqueous dispersion obtained by mixing a polyurethane resin having a hydrophilic group, a monofunctional alkyl (meth)acrylate having an alkyl group of 4 to 22 carbon atoms, and a poly(meth)acrylate having 2 to 6 functional groups, dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate and the poly(meth)acrylate contained in the mixture.

[0009]

[11] Use of an aqueous dispersion comprising a polyurethane resin dispersed in an aqueous dispersion medium, the aqueous dispersion containing a (meth)acrylic polymer containing, as constituent components, a monofunctional alkyl (meth)acrylate having an alkyl group having 4 to 22 carbon atoms and a poly(meth)acrylate having 2 to 6 functional groups, as a release coating agent for polyester substrates.

[0010] According to an embodiment of the present invention, a release coating agent for polyester substrates that has excellent adhesion to polyester substrates and heat-resistant peelability can be provided.

[0011] The release coating agent for polyester substrates according to this embodiment (hereinafter also simply referred to as a release coating agent) is a release coating agent containing an aqueous dispersion of a polyurethane resin, and the aqueous dispersion contains a specific (meth)acrylic polymer. Therefore, the release coating agent contains an aqueous dispersion medium, a polyurethane resin, and a (meth)acrylic polymer.

[0012] In this specification, "(meth)acrylic polymer" means an acrylic polymer and / or a methacrylic polymer. Similarly, "alkyl (meth)acrylate" means alkyl acrylate and / or alkyl methacrylate, and "poly(meth)acrylate" means polyacrylate and / or polymethacrylate. The same applies to other terms such as "(meth)acrylic" and "(meth)acrylate."

[0013] [Aqueous Dispersion Medium] The aqueous dispersion medium is a dispersion medium containing water, and examples thereof include water or a mixed medium of water and a hydrophilic organic solvent. From the viewpoint of dispersion stability of the aqueous dispersion, the aqueous dispersion medium is preferably water, and an organic solvent may be contained, but preferably in a small amount. In one embodiment, the aqueous dispersion medium preferably contains 70% by mass or more of water, more preferably 80% by mass or more of water, more preferably 90% by mass or more of water, and may be 100% by mass of water. That is, in the aqueous dispersion medium, the mass ratio of water / hydrophilic organic solvent is preferably 70 / 30 to 100 / 0, more preferably 80 / 20 to 100 / 0, and even more preferably 90 / 10 to 100 / 0.

[0014] As the hydrophilic organic solvent, various organic solvents that are soluble in water can be used, and examples thereof include lower monohydric alcohols such as methanol, ethanol, and propanol; polyhydric alcohols such as ethylene glycol and glycerin; and aprotic polar solvents such as N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and acetonitrile.

[0015] [Polyurethane Resin] A polyurethane resin is obtained by reacting a polyol with a polyisocyanate, and is a polymer having a urethane bond in the molecule. That is, a polyurethane resin contains a polyol and a polyisocyanate as its constituent components. Here, "containing a polyol as a constituent component" means that the polyurethane resin is used as a raw material (monomer) for synthesizing the polyurethane resin, and the polyurethane resin has a structure derived from this.

[0016] The polyurethane resin may have a hydrophilic group, and various water-based polyurethane resins such as anionic polyurethane resins, cationic polyurethane resins, and nonionic polyurethane resins may be used. The hydrophilic group may be an anionic group, a cationic group, or a hydrophilic segment.

[0017] The anionic polyurethane resin is a water-based polyurethane resin having an anionic group. Examples of the anionic group include at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphate group, and salts thereof. Examples of the salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts, ammonium salts, and amine salts such as primary amines, secondary amines, and tertiary amines.

[0018] The cationic polyurethane resin is a water-based polyurethane resin having cationic groups, such as quaternary ammonium groups.

[0019] Nonionic polyurethane resins are non-charged water-based polyurethane resins that do not have anionic or cationic groups, such as polyurethane resins having hydrophilic segments such as polyoxyethylene groups.

[0020] Examples of polyols constituting the polyurethane resin include polymer polyols such as polyester polyols (e.g., aliphatic polyester polyols, aromatic polyester polyols), polycarbonate polyols, polyether polyols (e.g., polytetramethylene glycol), and polybutadiene polyols. Any of these may be used alone or in combination of two or more.

[0021] The molecular weight of the polymer polyol is not particularly limited, and may be, for example, 500 to 5,000 in number average molecular weight (Mn), 800 to 4,000, or 1,000 to 3,000.

[0022] In this specification, the number average molecular weight (Mn) is a value measured by GPC (gel permeation chromatography) and calculated using a calibration curve of standard polystyrene. Specifically, the GPC conditions are as follows: column: "TSKgel G4000HXL + TSKgel G3000HXL + TSKgel G2000HXL + TSKgel G1000HXL + TSKgel G1000HXL" manufactured by Tosoh Corporation, mobile phase: THF (tetrahydrofuran), mobile phase flow rate: 1.0 mL / min, column temperature: 40°C, sample injection amount: 50 μL, sample concentration: 0.2 mass%.

[0023] As the polyol constituting the polyurethane resin, in addition to or in addition to the above polymer polyols, for example, low molecular weight polyhydric alcohols (preferably dihydric alcohols or trihydric alcohols) such as ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, bisphenol A, bisphenol F, bisphenol S, hydrogenated bisphenol A, trimethylolpropane, glycerin, and pentaerythritol may be used. Any of these may be used alone, or two or more may be used in combination.

[0024] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyester polyol to enhance the effect of improving adhesion to polyester substrates. That is, the polyurethane resin preferably contains a polyol containing a polyester polyol as a constituent component. The amount of polyester polyol in the polyol is, for example, preferably 30% by mass or more, more preferably 60% by mass or more, even more preferably 70 to 99% by mass, and may be 80 to 95% by mass, relative to 100% by mass of the polyol.

[0025] In this specification, when the amount of each component constituting a polyol is calculated based on 100% by mass of the polyol, if the polyol contains an anionic group as described below, the anionic group is considered to be in acid form. The amount of the anionic group-containing polyol is also calculated based on the anionic group as acid form. Furthermore, if the polyol contains a cationic group as described below, the amount is calculated using the amount of the polyol before the cationic group is neutralized with an acid or quaternized with a quaternizing agent.

[0026] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyol having three or more functional groups. This introduces a crosslinked structure into the polyurethane resin, thereby improving the water resistance of the release layer. Examples of polyols having three or more functional groups include polyhydric alcohols having three or more hydroxy groups, such as trimethylolpropane, and also include the above-mentioned polymer polyols having three or more hydroxy groups in the molecule.

[0027] The amount of the polyol having three or more functional groups in the polyol is not particularly limited, and may be, for example, 0.1 to 10% by mass, 0.5 to 8% by mass, or 1 to 5% by mass relative to 100% by mass of the polyol.

[0028] Examples of polyisocyanates constituting the polyurethane resin include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Any of these may be used alone or in combination of two or more.

[0029] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0030] Examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane.

[0031] Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and naphthalene diisocyanate.

[0032] In addition, isocyanurate, adduct, biuret, allophenate, carbodiimide, etc. of these polyisocyanates may be used. These polyisocyanates may be used alone or in combination of two or more.

[0033] In one embodiment, the polyurethane resin is preferably an anionic polyurethane resin obtained by reacting a polyol containing an anionic group-free polyol and an anionic group-containing polyol with a polyisocyanate. Examples of such anionic polyurethane resins include the following (A) and (B). Of these, the chain-extended type (A) is advantageous in improving the water resistance of the release layer.

[0034] (A) An anionic polyurethane resin obtained by synthesizing an isocyanate group-containing urethane prepolymer from an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate, and then chain-extending the urethane prepolymer with a chain extender.

[0035] (B) A hydroxy group-containing anionic polyurethane resin obtained by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate.

[0036] The anionic group-free polyol used to synthesize the anionic polyurethane resin can be any of the various polyols listed above that does not contain an anionic group or a cationic group. The anionic group-containing polyol is preferably a carboxyl group-containing polyol having a carboxyl group in the molecule, such as dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dioxymaleic acid, 2,6-dioxybenzoic acid, and 3,4-diaminobenzoic acid, as well as derivatives and salts thereof. These compounds may be used alone or in combination.

[0037] Here, the concept of anionic group includes not only the acid type (in the case of a carboxy group: —COOH) but also the salt type (in the case of a carboxy group: a carboxylate group represented by —COOX, where X is a cation that forms a salt with the carboxylic acid), and the acid type and the salt type may be mixed. By neutralizing the anionic group to form a salt, the polyurethane resin finally obtained can be made water-dispersible. Therefore, in an aqueous dispersion of the polyurethane resin, the anionic group may exist as a salt type. On the other hand, in the state of a coating film obtained by drying the aqueous dispersion, the anionic group may exist as a salt type when a non-volatile base is used as a neutralizing agent, or may exist as an acid type when a volatile base is used as a neutralizing agent.

[0038] In the anionic polyurethane resin, the amount of the anionic group-free polyol in the polyol is not particularly limited and may be, for example, 75 to 99% by mass, 80 to 97% by mass, or 85 to 95% by mass relative to 100% by mass of the polyol. The amount of the anionic group-containing polyol in the polyol is not particularly limited and may be, for example, 1 to 25% by mass, 3 to 20% by mass, or 5 to 15% by mass relative to 100% by mass of the polyol.

[0039] In one embodiment, the polyurethane resin may be a cationic polyurethane resin obtained by reacting a polyol containing a cationic group-free polyol and a cationic group-containing polyol with a polyisocyanate. Examples of such cationic polyurethane resins include the following (C).

[0040] (C) A cationic polyurethane resin obtained by synthesizing an isocyanate group-containing urethane prepolymer from a cationic group-free polyol, a cationic group-containing polyol, and a polyisocyanate, and then chain-extending the urethane prepolymer with a chain extender.

[0041] The cationic group-free polyol used to synthesize the cationic polyurethane resin can be a polyol that does not have an anionic group or a cationic group, among the various polyols listed above. Examples of cationic group-containing polyols include alkyldialkanolamines such as N-methyldiethanolamine and N-ethyldiethanolamine, and these can also be quaternized with an acid or a quaternizing agent. Examples of cationic groups include tertiary or quaternary ammonium groups, which are formed by neutralizing a tertiary amino group with an acid or quaternizing it with a quaternizing agent. Furthermore, the cationic group-containing polyol may be a tertiary amine group-containing compound capable of forming a tertiary or quaternary ammonium group.

[0042] In the cationic polyurethane resin, the amount of the cationic group-free polyol in the polyol is not particularly limited and may be, for example, 75 to 97% by mass or 80 to 95% by mass relative to 100% by mass of the polyol. The amount of the cationic group-containing polyol in the polyol is not particularly limited and may be, for example, 3 to 25% by mass or 5 to 20% by mass relative to 100% by mass of the polyol.

[0043] In one embodiment, the polyurethane resin may be a nonionic polyurethane resin obtained by reacting a polyol containing a hydrophilic segment and a polyol not containing a hydrophilic segment with a polyisocyanate. Examples of such nonionic polyurethane resins include the following (D).

[0044] (D) A nonionic polyurethane resin obtained by synthesizing an isocyanate group-containing urethane prepolymer from a hydrophilic segment-containing polyol, a hydrophilic segment-free polyol, and a polyisocyanate, and then chain-extending the urethane prepolymer with a chain extender.

[0045] Examples of the hydrophilic segment-containing polyol include polyols having a nonionic hydrophilic segment such as a polyoxyethylene group. Examples of the hydrophilic segment-free polyol include polyols from the various polyols listed above that do not have an anionic group, a cationic group, or a hydrophilic segment.

[0046] In the nonionic polyurethane resin, the amount of the hydrophilic segment-containing polyol in the polyol is not particularly limited and may be, for example, 5 to 60% by mass or 10 to 50% by mass relative to 100% by mass of the polyol. The amount of the hydrophilic segment-free polyol is also not particularly limited and may be, for example, 40 to 95% by mass or 50 to 90% by mass relative to 100% by mass of the polyol.

[0047] The chain extender that extends the chain of the isocyanate group-containing urethane prepolymer is not particularly limited, and examples thereof include water, and also polyvalent amine compounds such as aliphatic polyamine compounds (e.g., ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine), aromatic polyamine compounds (e.g., metaxylenediamine, tolylenediamine, diaminodiphenylmethane), alicyclic polyamine compounds (e.g., piperazine, isophoronediamine), and polyhydrazide compounds (e.g., hydrazine, adipic acid dihydrazide).

[0048] [(Meth)acrylic polymer] The (meth)acrylic polymer contains, as constituent components, a monofunctional alkyl (meth)acrylate (X) having an alkyl group with 4 to 22 carbon atoms and a poly(meth)acrylate (Y) having a functionality of 2 to 6. Here, with regard to the (meth)acrylic polymer, "containing as a constituent component" means that the (meth)acrylic polymer is used as a raw material (monomer) for synthesizing the polymer, and the (meth)acrylic polymer has a structure derived from this.

[0049] When the alkyl group of the alkyl (meth)acrylate (X) has 4 or more carbon atoms, the initial releasability can be improved, and when the alkyl group has 22 or less carbon atoms, the deterioration of releasability due to heating can be suppressed. The number of carbon atoms in the alkyl is preferably 6 to 20, more preferably 8 to 18, and even more preferably 10 to 16. The alkyl (meth)acrylate (X) may be a mixture of alkyl groups having different numbers of carbon atoms.

[0050] The alkyl group of the alkyl (meth)acrylate (X) may be a branched chain, but is preferably a linear alkyl group from the viewpoints of releasability, heat releasability, and water resistance.

[0051] Specific examples of the alkyl (meth)acrylate (X) include n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, n-icosyl (meth)acrylate, and n-docosyl (meth)acrylate. Any of these may be used alone, or two or more may be used in combination.

[0052] Poly(meth)acrylate refers to an ester compound having two or more (meth)acryloyl groups. Therefore, poly(meth)acrylate (Y) having 2 to 6 functional groups is a (meth)acrylic acid ester having 2 to 6 (meth)acryloyl groups per molecule. Use of such poly(meth)acrylate (Y) can improve heat peel resistance.

[0053] In one embodiment, the poly(meth)acrylate (Y) preferably has an acrylic equivalent, which is the molecular weight per functional group, of 80 to 150, and more preferably has an acrylic equivalent of 90 to 150.

[0054] Specific examples of the poly(meth)acrylate (Y) include (poly)alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Any of these may be used alone or in combination of two or more.

[0055] Among these, (poly)alkylene glycol di(meth)acrylate is preferred as the poly(meth)acrylate (Y). Here, "(poly)alkylene glycol" means monoalkylene glycol and / or polyalkylene glycol. The "poly" (number of repeating bonds) of the polyalkylene glycol is preferably 2 to 3, and the number of carbon atoms in the "alkylene" is preferably 2 to 4.

[0056] The (meth)acrylic polymer is a copolymer of an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y), and may be composed of only these (X) and (Y), or may contain other monomers as constituent components within a range that does not impair the effects of this embodiment. The total amount of the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in 100% by mass of all constituent components of the (meth)acrylic polymer is preferably 80% by mass or more, more preferably 90% by mass or more.

[0057] The ratio of the alkyl (meth)acrylate (X) to the poly(meth)acrylate (Y) in the (meth)acrylic polymer is not particularly limited, but the amount of poly(meth)acrylate (Y) relative to 100 parts by mass of the alkyl (meth)acrylate (X) is preferably 0.3 to 50 parts by mass, more preferably 1 to 30 parts by mass, and even more preferably 5 to 20 parts by mass. When the amount of poly(meth)acrylate (Y) is 50 parts by mass or less, the initial releasability can be improved, and when it is 0.3 parts by mass or more, the effect of improving heat releasability can be enhanced.

[0058] Polymerization of the monomer containing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) may be carried out by adding a known polymerization initiator. Examples of the polymerization initiator that can be used include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine), and substituted ethane initiators such as phenyl-substituted ethane. Alternatively, a redox initiator may be used which is a combination of a peroxide-based initiator such as a persulfate such as potassium persulfate, sodium persulfate, or ammonium persulfate, or a peroxide such as hydrogen peroxide, t-butyl hydroperoxide, or cumene hydroperoxide, and a reducing agent such as a sulfite such as sodium sulfite, a hydrogen sulfite such as sodium hydrogen sulfite, a metal salt such as cuprous sulfate or ferrous sulfate, or an organic reducing agent such as L-ascorbic acid.

[0059] The amount of the polymerization initiator is not particularly limited, and may be, for example, 0.005 to 1 part by mass per 100 parts by mass of all monomers including the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y).

[0060] [Aqueous Dispersion of Polyurethane Resin] The aqueous dispersion of polyurethane resin is an aqueous dispersion in which polyurethane resin is dispersed in an aqueous dispersion medium, and contains the above-mentioned (meth)acrylic polymer.

[0061] In the aqueous dispersion, the (meth)acrylic polymer is preferably contained in polyurethane resin particles. That is, the (meth)acrylic polymer is preferably contained together with the polyurethane resin in individual resin particles as dispersoids. In this case, the (meth)acrylic polymer may be present inside the particles, on the particle surface, or both inside and on the particle surface. While polyurethane resin has hydrophilic groups, (meth)acrylic polymers are hydrophobic and therefore more likely to be present inside the particles. Therefore, it is preferable that the (meth)acrylic polymer is present inside the particles and that the polyurethane resin having hydrophilic groups is present on the particle surface so as to cover it, thereby enhancing the effects of this embodiment.

[0062] The content of the polyurethane resin in the aqueous dispersion is not particularly limited, and may be, for example, 10 to 50% by mass, 15 to 45% by mass, or 20 to 40% by mass relative to the total mass of the aqueous dispersion.

[0063] The content of the (meth)acrylic resin is preferably set as follows in terms of the content of alkyl (meth)acrylate: That is, the amount of alkyl (meth)acrylate is preferably 40 to 350 parts by mass, more preferably 45 to 300 parts by mass, even more preferably 60 to 200 parts by mass, and even more preferably 70 to 150 parts by mass, per 100 parts by mass of polyurethane resin. When the content of alkyl (meth)acrylate is 40 parts by mass or more, releasability and water resistance can be improved, and when it is 350 parts by mass or less, adhesion to polyester substrates can be improved.

[0064] The size of the resin particles in the aqueous dispersion is not particularly limited, and may be, for example, an average particle diameter of 0.001 to 0.5 μm. Here, the average particle diameter is the 50% cumulative particle diameter (d50) measured using a "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0065] The aqueous dispersion of the polyurethane resin may contain other components as long as the effects of the aqueous dispersion are not impaired. For example, it may contain a crosslinking agent for crosslinking the polyurethane resin, a surfactant for dispersing the polyurethane resin, the (meth)acrylic resin, or a monomer thereof in an aqueous dispersion medium, a polymerization initiator for polymerizing the (meth)acrylic resin, etc.

[0066] Examples of crosslinking agents include compounds having two or more reactive groups in the molecule that can react with at least one active hydrogen-containing group selected from the group consisting of a hydroxy group, a primary amino group, a secondary amino group, and a thiol group contained in the polyurethane resin. This can improve the water resistance of the release layer formed by the release coating agent. If the polyurethane resin has a carboxy group, the crosslinking agent can also crosslink with the carboxy group.

[0067] Examples of the crosslinking agent include carbodiimide compounds, oxazoline compounds, blocked isocyanate compounds, and epoxy compounds, and these may be used alone or in combination of two or more.

[0068] The amount of the crosslinking agent is not particularly limited, and may be, for example, 1.0 to 20 parts by mass per 100 parts by mass of the polyurethane resin.

[0069] The surfactant is not particularly limited, and anionic surfactants and nonionic surfactants are preferably used. Examples of anionic surfactants include polyoxyalkylene alkyl ether sulfates, polyoxyalkylene styrenated phenyl ether sulfates, and polyoxyalkylene alkyl ether phosphates. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyethylene styrenated phenyl ethers, polyoxyethylene phenyl ethers, and polyoxyethylene polyoxypropylene glycols.

[0070] The amount of the surfactant is not particularly limited, and may be, for example, 0.1 to 5.0 parts by mass per 100 parts by mass of the total amount of the polyurethane resin and the (meth)acrylic polymer.

[0071] [Method for Producing Aqueous Dispersion] The method for producing the aqueous dispersion of polyurethane resin is not particularly limited, and it may be produced, for example, by a method including the following steps (1) to (4).

[0072] Step (1): A step of reacting a polyol with a polyisocyanate. Step (2): A step of mixing the polyurethane resin having a hydrophilic group obtained in Step (1), an alkyl (meth)acrylate (X), and a poly(meth)acrylate (Y). Step (3): A step of dispersing the mixture in an aqueous dispersion medium. Step (4): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) contained in the mixture dispersed in the aqueous dispersion medium.

[0073] In this way, it is believed that by mixing a polyurethane resin having a hydrophilic group with the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y), dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture in the dispersed state, it is possible to efficiently incorporate the (meth)acrylic polymer into the interior of the polyurethane resin particles.

[0074] In the above step (1), the reaction between the polyol and the polyisocyanate may be carried out without an organic solvent, or may be carried out in an organic solvent having no active hydrogen groups, such as methyl ethyl ketone or acetone. The polyurethane resin obtained by the reaction in step (1) also encompasses the urethane prepolymer before chain extension, etc. Therefore, in step (2), such a urethane prepolymer may be mixed with the acrylic monomers containing the above (X) and (Y).

[0075] Furthermore, when the polyurethane resin has an anionic group or a cationic group, the anionic group or the cationic group may be neutralized with a neutralizing agent or the cationic group may be quaternized with a quaternizing agent before or after mixing the polyurethane resin with the acrylic monomer in step (2).

[0076] Examples of bases that neutralize the anionic group include non-volatile bases such as sodium hydroxide and potassium hydroxide, tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine and triethanolamine, and volatile bases such as ammonia.

[0077] Examples of acids that neutralize cationic groups include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, malic acid, and malonic acid. Examples of quaternizing agents that quaternize cationic groups include alkyl halides such as methyl chloride and methyl bromide, and dialkyl sulfates such as dimethyl sulfate and diethyl sulfate.

[0078] The method for dispersing the mixture in the aqueous dispersion medium in step (3) is not particularly limited, and examples thereof include (i) a method in which the mixture or a resin solution thereof is added to the aqueous dispersion medium while stirring it with a homogenizer, homomixer, etc., and (ii) a method in which the aqueous dispersion medium is added to the mixture or a resin solution thereof while stirring it with a homogenizer, homomixer, etc. A surfactant may be added to facilitate emulsification and dispersion of the mixture containing the polyurethane resin and the acrylic monomer in the aqueous dispersion medium.

[0079] When a urethane prepolymer is synthesized in step (1), the chains of the urethane prepolymer may be extended with a chain extender after or during dispersion in step (3). The chain extension reaction may be carried out simultaneously with or before the polymerization reaction in step (4).

[0080] The polymerization in step (4) may be thermal polymerization, but is preferably carried out by adding a polymerization initiator. The polymerization temperature is adjusted depending on the type of polymerization initiator and may be, for example, 20°C to 100°C.

[0081] When the reaction between the polyol and the polyisocyanate is carried out in an organic solvent in step (1), the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (3) or after the polymerization reaction in step (4).

[0082] In one embodiment, when the anionic polyurethane resin (A) is used as the polyurethane resin, the polyurethane resin may be produced by the following steps (a1) to (a6). Step (a1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate. Step (a2): A step of neutralizing the anionic groups of the isocyanate group-containing urethane prepolymer. Step (a3): A step of mixing the isocyanate group-containing urethane prepolymer with an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y). Step (a4): A step of dispersing the mixture in an aqueous dispersion medium. Step (a5): A step of chain-extending the isocyanate group-containing urethane prepolymer in the mixture dispersed in the aqueous dispersion medium with a chain extender. Step (a6): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in the aqueous dispersion medium.

[0083] Step (a1) corresponds to the above step (1), step (a3) ​​corresponds to the above step (2), step (a4) corresponds to the above step (3), step (a6) corresponds to the above step (4), and steps (a2) and (a5) are additional steps.

[0084] In step (a1), the polyisocyanate is used so that the amount of isocyanate groups is stoichiometrically in excess of the amount of hydroxy groups contained in the polyol, for example, so that the equivalent ratio of hydroxy groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0085] The order of steps (a2) and (a3) ​​does not matter. In step (a5), the chain extender may be added after or during the dispersion of the polyurethane prepolymer in the aqueous dispersion medium in step (a4). The chain extender is as described above, and water also serves as a chain extender. When water is used as the chain extender, the water in the aqueous dispersion medium also serves as the chain extender.

[0086] In one embodiment, when the anionic polyurethane resin (B) is used as the polyurethane resin, the polyurethane resin may be produced by the following steps (b1) to (b5). Step (b1): A step of synthesizing a hydroxy group-containing polyurethane resin by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate. Step (b2): A step of neutralizing the anionic groups of the hydroxy group-containing polyurethane resin. Step (b3): ​​A step of mixing the hydroxy group-containing polyurethane resin with an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y). Step (b4): A step of dispersing the mixture in an aqueous dispersion medium. Step (b5): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in the aqueous dispersion medium.

[0087] Step (b1) corresponds to the above step (1), step (b3) corresponds to the above step (2), step (b4) corresponds to the above step (3), step (b5) corresponds to the above step (4), and step (b2) is an additional step.

[0088] In step (b1), the polyol is used so that the amount of hydroxy groups is stoichiometrically in excess of the amount of isocyanate groups contained in the polyisocyanate, for example, so that the equivalent ratio of hydroxy groups to isocyanate groups (NCO / OH) is 0.70 to 0.95 (more preferably 0.75 to 0.90). The order of steps (b2) and (b3) does not matter.

[0089] In one embodiment, when the cationic polyurethane resin (C) above is used as the polyurethane resin, the polyurethane resin may be produced by the following steps (c1) to (c6). Step (c1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting a cationic group-free polyol, a cationic group-containing polyol, and a polyisocyanate. Step (c2): A step of neutralizing the cationic groups of the isocyanate group-containing urethane prepolymer with an acid or quaternizing it with a quaternizing agent. Step (c3): A step of mixing the isocyanate group-containing urethane prepolymer with an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y). Step (c4): A step of dispersing the mixture in an aqueous dispersion medium. Step (c5): A step of chain-extending the isocyanate group-containing urethane prepolymer in the mixture dispersed in the aqueous dispersion medium with a chain extender. Step (c6): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in the aqueous dispersion medium.

[0090] Step (c1) corresponds to the above step (1), step (c3) corresponds to the above step (2), step (c4) corresponds to the above step (3), step (c6) corresponds to the above step (4), and steps (c2) and (c5) are additional steps.

[0091] The order of steps (c2) and (c3) does not matter. The equivalent ratio of the hydroxy group to the isocyanate group in step (c1), the timing of adding the chain extender in step (c5), and the case where water is used as the chain extender are the same as those in steps (a1) and (a5).

[0092] In one embodiment, when the nonionic polyurethane resin (D) is used as the polyurethane resin, the polyurethane resin may be produced by the following steps (d1) to (d5). Step (d1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting a hydrophilic segment-containing polyol, a hydrophilic segment-free polyol, and a polyisocyanate. Step (d2): A step of mixing the isocyanate group-containing urethane prepolymer with an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y). Step (d3): A step of dispersing the mixture in an aqueous dispersion medium. Step (d4): A step of chain-extending the isocyanate group-containing urethane prepolymer dispersed in the aqueous dispersion medium with a chain extender. Step (d5): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in the aqueous dispersion medium.

[0093] Step (d1) corresponds to the above-mentioned step (1), step (d2) corresponds to the above-mentioned step (2), step (d3) corresponds to the above-mentioned step (3), step (d5) corresponds to the above-mentioned step (4), and step (d4) is an additional step. The equivalent ratio of hydroxy groups to isocyanate groups in step (d1), as well as the timing of adding the chain extender and the use of water as the chain extender in step (d4), are the same as those in the above-mentioned steps (a1) and (a5).

[0094] [Release Coating Agent for Polyester Substrate] The release coating agent for polyester substrate according to this embodiment contains the aqueous dispersion, and therefore contains an aqueous dispersion medium, a polyurethane resin, and a (meth)acrylic resin. The release coating agent may consist of only the aqueous dispersion, or may contain various additives such as an antioxidant, an antistatic agent, a surfactant, an antifoaming agent, and a surface conditioner in addition to the aqueous dispersion.

[0095] The content of the polyurethane resin in the release coating agent is not particularly limited, and may be, for example, 10 to 50% by mass, 15 to 45% by mass, or 20 to 40% by mass relative to the total mass of the release coating agent.

[0096] [Release Sheet] A release sheet according to one embodiment includes a polyester substrate and a release layer provided on the polyester substrate, and the release layer is formed from the release coating agent.

[0097] The polyester substrate may be formed from various polyesters containing dicarboxylic acid and diol as constituent components (monomers). Examples of polyester substrates include polyethylene terephthalate (PET) substrates, polyethylene naphthalate (PEN) substrates, polyethylene furanoate (PEF) substrates, polytrimethylene terephthalate (PTT) substrates, polybutylene terephthalate (PBT) substrates, and polybutylene naphthalate (PBN) substrates. Among these, polyester substrates formed from polyesters containing aromatic dicarboxylic acid and ethylene glycol as constituent components, specifically PET substrates, PEN substrates, and PEF substrates, are more preferably used.

[0098] The polyester substrate may be in the form of a film or a plate, and the thickness is not particularly limited. The polyester substrate may be subjected to a surface treatment such as a corona surface treatment.

[0099] The release layer is a resin layer laminated on at least one of the front and back surfaces of the polyester substrate, and can be formed by applying a release coating agent to the polyester substrate and drying it. If the release coating agent contains the above-mentioned crosslinking agent, the polyurethane resin is crosslinked by applying the release coating agent and then performing a heat treatment such as drying.

[0100] The thickness (dry film thickness) of the release layer is not particularly limited, and may be, for example, 0.01 to 50 μm, or 0.05 to 10 μm.

[0101] The release sheet can be used, for example, as a process protection film, and is attached to an adhesive or non-adhesive object to protect the object. When the object to which the release sheet is attached is used, the release sheet is peeled off. The peeled release sheet may be discarded.

[0102] [Laminate] A laminate according to one embodiment includes the release sheet and a resin layer releasably provided on the release layer. The release sheet is used, for example, as (1) a protective sheet for protecting the pressure-sensitive adhesive film, or as (2) a support sheet for forming a resin film.

[0103] In the case of the protective sheet (1) above, the release sheet is used to protect a product having a pressure-sensitive adhesive film formed on its surface, and the release sheet is attached to the adhesive surface of the product on which the pressure-sensitive adhesive film is formed. Therefore, the pressure-sensitive adhesive film corresponds to the resin layer, and the product and the release sheet attached to its adhesive surface constitute the laminate. The release sheet is peeled off from the adhesive surface when the product is used. Examples of such products include liquid crystal polarizing plates.

[0104] In the case of the support sheet (2) above, a resin liquid is applied or poured onto the release layer of the release sheet and cured by drying or the like to form a resin film. Therefore, the resin film corresponds to the resin layer, and the release sheet provided with the resin film corresponds to the laminate. The release sheet is peeled off from the resin film when the resin film is to be used.

[0105] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0106] Details of each component used in the examples are as follows:

[0107] [Polyol] Polyester polyol 1: Aromatic polyester diol (number of functional groups: 2, number average molecular weight: 2000). The synthesis method was as follows: 54.72 parts by mass of isophthalic acid, 8.63 parts by mass of adipic acid, 23.89 parts by mass of neopentyl glycol, and 12.76 parts by mass of ethylene glycol were charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, and the temperature was raised to 250°C while stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less, yielding an aromatic polyester diol.

[0108] Polyester polyol 2: Aromatic polyester diol (number of functional groups: 2, number average molecular weight: 2000). The synthesis method was as follows: 52.41 parts by mass of terephthalic acid, 8.77 parts by mass of adipic acid, 26.58 parts by mass of 1,6-hexanediol, and 12.24 parts by mass of ethylene glycol were charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, and the temperature was raised to 250°C while stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less, yielding an aromatic polyester diol.

[0109] Polycarbonate polyol: polycarbonate diol (number of functional groups: 2, number average molecular weight: 2000), "UH-200" manufactured by UBE Co., Ltd. Bisphenol-type polyol: EO adduct of bisphenol A (number of functional groups: 2, number average molecular weight: 325), "Newpol BPE-20NK" manufactured by Sanyo Chemical Industries, Ltd. Trifunctional polyol: trimethylolpropane (number of functional groups: 3), manufactured by Mitsui Gas Chemical Industry Co., Ltd. POE-containing polyol: polyoxyethylene group-containing nonionic polyol (number of functional groups: 2, number average molecular weight: 600), "Ymer N180" manufactured by Perstorp Cationic group-containing polyol: N-methyldiethanolamine, manufactured by Tokyo Chemical Industry Co., Ltd. Dimethylolpropionic acid: "Bis-MPA (registered trademark)" manufactured by Perstorp (number of functional groups: 2)

[0110] [Polyisocyanate] IPDI: isophorone diisocyanate (number of functional groups: 2, molecular weight: 222.3), "VESTANAT (registered trademark) IPDI" manufactured by Evonik Hydrogenated MDI: dicyclohexylmethane 4,4'-diisocyanate (number of functional groups: 2, molecular weight: 262), "VESTANAT (registered trademark) H12MDI" manufactured by Evonik HDI: hexamethylene diisocyanate (number of functional groups: 2, molecular weight: 168.2), "Duranate (registered trademark) 50M-HDI" manufactured by Asahi Kasei Corporation

[0111] [(Meth)acrylic acid esters] n-Butyl acrylate: "Butyl acrylate" manufactured by Mitsubishi Chemical Corporation n-Octyl acrylate: "NOAA" manufactured by Osaka Organic Chemical Industry Ltd. n-Dodecyl acrylate: "LA" manufactured by Osaka Organic Chemical Industry Ltd. Stearyl acrylate: "STA" manufactured by Osaka Organic Chemical Industry Ltd. n-Dodecyl methacrylate: "Light Ester L" manufactured by Kyoeisha Chemical Co., Ltd. 2-Ethylhexyl acrylate: manufactured by Mitsubishi Chemical Corporation Ethyl acrylate: manufactured by Mitsubishi Chemical Corporation

[0112] [Poly(meth)acrylate] Dimethacrylate 1: ethylene glycol dimethacrylate, "Light Ester EG" manufactured by Kyoeisha Chemical Co., Ltd. Dimethacrylate 2: triethylene glycol dimethacrylate, "Light Ester 3EG" manufactured by Kyoeisha Chemical Co., Ltd. Hexaacrylate: dipentaerythritol hexaacrylate (DPHA), "Light Acrylate DPE-6A" manufactured by Kyoeisha Chemical Co., Ltd.

[0113] [Other additives] Surfactant: "Hitenol (registered trademark) LA-12" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Crosslinking agent: "V02-L02" manufactured by Nisshinbo Chemical Inc. (non-volatile content 40%, NCN equivalent 385) Polymerization initiator 1: tert-butyl hydroperoxide (70% aqueous solution) manufactured by Tokyo Chemical Industry Co., Ltd. Polymerization initiator 2: sodium sulfite manufactured by Nacalai Tesque, Inc.

[0114] The evaluation method for the release coating agent is as follows.

[0115] [Releasability 1A (Initial Releasability from Acrylic Pressure-Sensitive Adhesive)] A corona-discharge-treated PET substrate ("Lumirror T-60," manufactured by Toray Industries, Inc.) was used as the PET substrate. A release coating agent was applied to the PET substrate using a bar coater to a dry film thickness of 1 μm, and the PET substrate was dried at 160°C for 1 minute to obtain a test piece (coated film) on which a coating film of the release coating agent was formed. However, in Comparative Example 3, a PP substrate ("Torayfan BO," manufactured by Toray Industries, Inc.) was used instead of the PET substrate. An acrylic pressure-sensitive adhesive tape "No. 31B" manufactured by Nitto Denko Corporation was attached to the coating film of the test piece using a 2 kg roller, and the peel strength (unit: mN / 25 mm) after 3 hours was measured. The peel strength was measured using a 180° peel test (300 mm / min) in accordance with JIS Z0237:2009. The smaller the peel strength, the better the releasability.

[0116] [Releasability 1B (heat-resistant peelability against acrylic adhesive, 70°C x 20 hours)] An acrylic adhesive tape "No. 31B" manufactured by Nitto Denko Corporation was applied to the coating film of a test piece prepared in the same manner as in Release Property 1A using a 2 kg roller, and heated at 70°C for 20 hours. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as in Release Property 1A. The smaller the peel strength, the more excellent the heat-resistant peelability. In the peel strength measurement, the case where the entire coating film peeled off was marked "F".

[0117] [1B / 1A] 1B / 1A is the ratio of the peel strength of Peelability 1B to the peel strength of Peelability 1A. The smaller this ratio, the less deterioration of releasability due to heating. In Peelability 1B, peeling together with the coating film was indicated by "F."

[0118] [Releasability 1C (heat-resistant peelability against acrylic adhesive, 150°C x 5 minutes)] An acrylic adhesive tape "No. 31B" manufactured by Nitto Denko Corporation was applied to the coating film of a test piece prepared in the same manner as in Release Property 1A using a 2 kg roller, and heated at 150°C for 5 minutes. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as in Release Property 1A. In the peel strength measurement, cases where the entire coating peeled off were marked with "F."

[0119] [1C / 1A] 1C / 1A is the ratio of the peel strength of Peelability 1C to the peel strength of Peelability 1A. The smaller this ratio, the less deterioration of releasability due to heating. In Peelability 1C, peeling together with the coating film was indicated by "F."

[0120] [Releasability 2A (Initial releasability from silicone-based adhesive)] A silicone-based adhesive tape "No. 336" manufactured by Nitto Denko Corporation was applied to the coating film of a test piece prepared in the same manner as in Release Property 1A using a 2 kg roller, and the peel strength (unit: mN / 25 mm) after 3 hours was measured. The peel strength was measured using a 180° peel test (300 mm / min) in accordance with JIS Z0237:2009. The smaller the peel strength, the better the releasability.

[0121] [Releasability 2B (heat-resistant peeling property for silicone-based adhesive, 70°C x 20 hours)] A silicone-based adhesive tape "No. 336" manufactured by Nitto Denko Corporation was applied to the coating film of a test piece prepared in the same manner as for Release Property 1A using a 2 kg roller, and heated at 70°C for 20 hours. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as for Release Property 2A. The smaller the peel strength, the more excellent the heat-resistant peeling property. In the peel strength measurement, the case where the entire coating film peeled off was marked "F".

[0122] [2B / 2A] 2B / 2A is the ratio of the peel strength of peelability 2B to the peel strength of peelability 2A. The smaller this ratio, the less deterioration of releasability due to heating. In peelability 2B, peeling of the entire coating film was indicated by "F."

[0123] [Releasability 2C (heat-resistant peelability against silicone-based adhesive, 150°C x 5 minutes)] A silicone-based adhesive tape "No. 336" manufactured by Nitto Denko Corporation was attached to the coating film of a test piece prepared in the same manner as for Release Property 1A using a 2 kg roller, and heated at 150°C for 5 minutes. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as for Release Property 2A. In the peel strength measurement, cases where the entire coating peeled off were marked with "F."

[0124] [2C / 2A] 2C / 2A is the ratio of the peel strength of peelability 2C to the peel strength of peelability 2A. The smaller this ratio, the less deterioration of releasability due to heating. In peelability 2C, peeling together with the coating film was indicated as "F."

[0125] [Adhesion] Test pieces with a release coating film formed thereon were obtained in the same manner as in Peelability 1A. The coating surface of the test piece was rubbed with a cotton swab moistened with isopropyl alcohol, and evaluated according to the following criteria. Here, rubbing was performed by lightly pressing the flat side of the cotton swab against the coating surface and moving it back and forth for about 2 cm (one back and forth was one rub), and the state after the first and second rubbings was observed. ⊚: No peeling even after the second rubbing. ◯: No peeling after the first rubbing, but peeling after the second rubbing. ×: Peeling after the first rubbing.

[0126] [Water Resistance] A release coating agent was poured onto a fluororesin-coated frying pan so that the dry film thickness was 500 μm, and then dried at 40° C. for 15 hours, at 80° C. for 6 hours, and then at 120° C. for 20 minutes to produce a film made of the release coating agent. The film was used as a test piece, and the test piece was immersed in warm water at 40° C. for 24 hours, and the mass of the film after immersion was measured. The increase (%) in mass after immersion relative to the initial mass before immersion was determined. The smaller the increase rate, the smaller the swelling in water and the better the water resistance.

[0127] [Example 1] In a four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 54.2 parts by weight of polyester polyol 1, 2.6 parts by weight of trifunctional polyol, 8.8 parts by weight of dimethylolpropionic acid, and 100 parts by weight of methyl ethyl ketone were added and thoroughly stirred and dissolved, and then 34.4 parts by weight of IPDI was added and reacted at 75 ° C. until the content of free isocyanate groups relative to the solid content was 2.9% by weight, to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. This methyl ethyl ketone solution was cooled to 45 ° C. and neutralized by adding 6.64 parts by weight of triethylamine as a neutralizing agent, and then 100 parts by weight of n-dodecyl acrylate, 10 parts by weight of dimethacrylate 1, 2.2 parts by weight of a surfactant, and 200 parts by weight of methyl ethyl ketone were added and mixed with stirring. Subsequently, while stirring using a homogenizer, 600 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse the mixture, and the dispersion was stirred at 40°C for 1 hour to complete the chain extension reaction with water. Thereafter, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and added, and the mixture was allowed to react at 35°C to 45°C for 3 hours to polymerize a (meth)acrylic polymer. Thereafter, methyl ethyl ketone was distilled off under heating and reduced pressure, and water was added to adjust the solids content, yielding a release coating agent consisting of an aqueous dispersion with a solids content of 30% by mass.

[0128] Examples 2 to 18, 20 to 21, and 25, and Comparative Examples 1 to 4. The types and amounts of polyol, polyisocyanate, and acrylic monomer, as well as the amounts of neutralizer and polymerization initiator 1 and 2, were changed as shown in Tables 1 and 2 below, and the remaining procedures were the same as in Example 1 to obtain release coating agents composed of aqueous dispersions in Examples 2 to 18, 20 to 21, and 25, and Comparative Examples 1 to 4. However, the amount of free isocyanate groups at the end of the urethane reaction to obtain the isocyanate group-containing urethane prepolymer was 2.9% by mass in Examples 2 to 3, 5 to 18, and Comparative Examples 1 to 4, 3.92% by mass in Example 4, 5.35% by mass in Example 20, 1.8% by mass in Example 21, and 2.3% by mass in Example 25. The amount of distilled water added as a dispersion medium was adjusted so that the solids concentration of the aqueous dispersion was 30% by mass.

[0129] [Example 19] To the dispersion after emulsification and dispersion, 1.87 parts by mass of ethylenediamine was added as a chain extender, and the mixture was stirred at 40°C for 1 hour to complete the chain extension reaction. The rest of the procedure was the same as in Example 1, and a release coating agent made of the aqueous dispersion of Example 19 was obtained.

[0130] Example 22 A release coating agent comprising the aqueous dispersion of Example 22 was obtained in the same manner as in Example 1, except that 550 parts by mass of distilled water and 50 parts by mass of N-methylpyrrolidone (NMP) were added instead of 600 parts by mass of distilled water as a dispersion medium, and after emulsification dispersion, chain extension reaction, polymerization reaction, and distillation of methyl ethyl ketone, water for adjusting the solid content was added to make the dispersion medium composition distilled water / NMP = 90 / 10 (mass ratio).

[0131] Example 23 A release coating agent made from the aqueous dispersion of Example 23 was obtained in the same manner as in Example 1, except that no surfactant was added.

[0132] [Example 24] A (meth)acrylic polymer was polymerized, and methyl ethyl ketone was distilled off. Then, 18.7 parts by mass of a crosslinking agent was added, and the other procedures were carried out in the same manner as in Example 1, to obtain a release coating agent comprising the aqueous dispersion of Example 24.

[0133] [Example 26] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 65.6 parts by weight of polyester polyol 1, 2.6 parts by weight of trifunctional polyol, 8.8 parts by weight of dimethylolpropionic acid, and 100 parts by weight of methyl ethyl ketone were added and thoroughly stirred and dissolved, and then 23 parts by weight of IPDI was added. The reaction was continued at 75 ° C. until the content of free isocyanate groups relative to the solids content was 0.05% by weight or less, to obtain a methyl ethyl ketone solution of a hydroxy group-containing polyurethane resin. This methyl ethyl ketone solution was cooled to 45 ° C. and neutralized by adding 6.64 parts by weight of triethylamine as a neutralizing agent. Then, 100 parts by weight of n-dodecyl acrylate, 10 parts by weight of dimethacrylate 1, 2.2 parts by weight of a surfactant, and 200 parts by weight of methyl ethyl ketone were added and mixed with stirring. Subsequently, while stirring using a homogenizer, 600 parts by weight of distilled water was added as a dispersion medium to emulsify and disperse the mixture. Thereafter, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and then added, and the mixture was allowed to react for 3 hours at 35 to 45° C. to polymerize a (meth)acrylic polymer. Thereafter, methyl ethyl ketone was distilled off under heating and reduced pressure, and water for adjusting the solids content was added to obtain a release coating agent consisting of an aqueous dispersion with a solids content of 30% by mass.

[0134] [Example 27] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 33.0 parts by weight of polyester polyol 1, 35.0 parts by weight of POE-containing polyol, 2.6 parts by weight of trifunctional polyol, and 100 parts by weight of methyl ethyl ketone were added and thoroughly stirred and dissolved, and then 29.4 parts by weight of IPDI was added, and the reaction was continued at 75 ° C. until the content of free isocyanate groups relative to the solids content reached 2.5% by weight, to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. After cooling this methyl ethyl ketone solution to 45 ° C., 100 parts by weight of n-dodecyl acrylate, 10 parts by weight of dimethacrylate 1, 2.2 parts by weight of a surfactant, and 200 parts by weight of methyl ethyl ketone were added and mixed with stirring. Subsequently, while stirring with a homogenizer, 600 parts by weight of distilled water was added as a dispersion medium to emulsify and disperse the mixture, and the dispersion was stirred at 40 ° C. for 1 hour, completing the chain extension reaction with water. Thereafter, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and then added, and the mixture was allowed to react for 3 hours at 35 to 45° C. to polymerize a (meth)acrylic polymer. Thereafter, methyl ethyl ketone was distilled off under heating and reduced pressure, and water for adjusting the solids content was added to obtain a release coating agent consisting of an aqueous dispersion with a solids content of 30% by mass.

[0135] [Example 28] A four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was added with 47.3 parts by weight of polyester polyol 1, 2.6 parts by weight of trifunctional polyol, 10.5 parts by weight of cationic group-containing polyol, and 100 parts by weight of methyl ethyl ketone was thoroughly stirred and dissolved, and then 39.6 parts by weight of IPDI was added, and the content of free isocyanate groups relative to the solids was allowed to react at 75 ° C. until 3.2% by weight, to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. This methyl ethyl ketone solution was cooled to 45 ° C., and 11.11 parts by weight of dimethyl sulfate was added as a quaternizing agent to quaternize it, followed by 100 parts by weight of n-dodecyl acrylate, 10 parts by weight of dimethacrylate 1, 2.2 parts by weight of a surfactant, and 200 parts by weight of methyl ethyl ketone were added and stirred and mixed. Subsequently, while stirring using a homogenizer, 600 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse the mixture, and the dispersion was stirred at 40°C for 1 hour to complete the chain extension reaction with water. Thereafter, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10-fold with distilled water and added, and the mixture was allowed to react at 35 to 45°C for 3 hours to polymerize a (meth)acrylic polymer. Thereafter, methyl ethyl ketone was distilled off under heating and reduced pressure, and water was added to adjust the solids content, yielding a release coating agent consisting of an aqueous dispersion with a solids content of 30% by mass.

[0136] The release coating agents of Examples 1 to 28 and Comparative Examples 1 to 4 were evaluated for releasability 1A, 1B, and 1C, releasability 2A, 2B, and 2C, adhesion, and water resistance. The results are shown in Tables 1 and 2.

[0137] In Tables 1 and 2, "Water" in the "Chain extender: ethylenediamine" column means that water was used as the chain extender, and "None" means that no chain extension was performed. "Amount of polyurethane resin" refers to the amount of polyurethane resin in the final aqueous dispersion, expressed in parts by mass relative to 100 parts by mass of the total of the polyol and isocyanate used as raw materials. "Index: NCO / OH" refers to the equivalent ratio of hydroxy groups to isocyanate groups in the urethane prepolymer. "Substrate" refers to the substrate used in the evaluation of peelability and adhesion, with "PET" meaning a PET substrate and "PP" meaning a PP substrate. The numerical value for the evaluation of peelability is peel strength (unit: mN / 25 mm).

[0138]

[0139]

[0140] As shown in Tables 1 and 2, Comparative Example 1 did not contain alkyl (meth)acrylate (X), and therefore had poor initial releasability and heat-resistant releasability. Comparative Example 2 used ethyl acrylate, whose alkyl group had two carbon atoms, as the alkyl (meth)acrylate, and therefore had poor initial releasability and heat-resistant releasability. Comparative Example 3 used a PP substrate, and therefore had poor adhesion of the release layer to the substrate. Comparative Example 4 did not contain poly(meth)acrylate (Y), and therefore had poor heat-resistant adhesion.

[0141] In contrast, Examples 1 to 28 exhibited excellent adhesion to PET substrates, suppressed deterioration of releasability due to heating, and exhibited heat-resistant peelability. Comparing Examples 1 and 2 with Examples 3 and 4, the use of polyester polyols improved initial releasability. Comparing Examples 1 and 2 with Examples 5 and 6, it was found that, from the standpoint of adhesion, alicyclic polyisocyanates are preferable to aliphatic polyisocyanates, with IPDI being more preferable. Comparing Examples 1 and 2 with Examples 7 and 8, it was found that increasing the number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (X) tends to improve initial releasability and water resistance; however, Example 9 shows that too many carbon atoms tends to decrease heat-resistant adhesion. Furthermore, the results of Examples 10 and 11 indicate that, as the alkyl (meth)acrylate (X), alkyl acrylates exhibit better initial releasability than alkyl methacrylates, and that linear alkyl groups exhibit better initial releasability than branched alkyl groups.

[0142] Unlike Example 1, Example 23 did not contain a surfactant, and the peelability, adhesion, and heat resistance were equivalent to those of Example 1, but some residue remained after filtration during preparation. In Example 24, a crosslinking agent was added to Example 1, and although the initial peelability tended to decrease slightly, water resistance was improved.

[0143] The various numerical ranges described in this specification can be arbitrarily combined with their respective upper and lower limit values, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0144] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. A release coating agent for polyester substrates, comprising an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, the aqueous dispersion comprising a (meth)acrylic polymer comprising, as constituent components, a monofunctional alkyl (meth)acrylate having an alkyl group with 4 to 22 carbon atoms and a poly(meth)acrylate having 2 to 6 functional groups.

2. The release coating agent for polyester substrates according to claim 1, wherein the (meth)acrylic polymer is contained in individual resin particles as a dispersoid together with the polyurethane resin.

3. The release coating agent for polyester substrates according to claim 1, wherein the (meth)acrylic polymer contains 0.3 to 50 parts by weight of the poly(meth)acrylate per 100 parts by weight of the alkyl (meth)acrylate.

4. The release coating agent for polyester substrates according to claim 1, wherein the alkyl group of the alkyl (meth)acrylate is a straight-chain alkyl group.

5. The release coating agent for polyester substrates according to claim 1, wherein the poly(meth)acrylate has an acrylic equivalent, which is the molecular weight per functional group, of 80 to 150.

6. The release coating agent for polyester substrates according to claim 1, wherein the amount of said alkyl (meth)acrylate is 40 to 350 parts by mass per 100 parts by mass of said polyurethane resin.

7. A release coating agent for polyester substrates according to claim 1, wherein the polyurethane resin contains a polyol including a polyester polyol as a constituent component, and the polyester polyol is contained in an amount of 30% by mass or more relative to 100% by mass of the polyol.

8. A release sheet comprising a polyester substrate and a release layer formed on the polyester substrate, the release layer comprising the release coating agent according to any one of claims 1 to 7.

9. A laminate comprising the release sheet according to claim 8 and a resin layer releasably provided on the release layer of the release sheet.

10. A release coating agent for polyester substrates, comprising an aqueous dispersion obtained by mixing a polyurethane resin having a hydrophilic group, a monofunctional alkyl (meth)acrylate having an alkyl group having 4 to 22 carbon atoms, and a poly(meth)acrylate having 2 to 6 functional groups, dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate and the poly(meth)acrylate contained in the mixture.

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